* Add configurable Trust Models

Gitea's default signature verification model differs from GitHub. GitHub
uses signatures to verify that the committer is who they say they are -
meaning that when GitHub makes a signed commit it must be the committer.
The GitHub model prevents re-publishing of commits after revocation of a
key and prevents re-signing of other people's commits to create a
completely trusted repository signed by one key or a set of trusted
keys.

The default behaviour of Gitea in contrast is to always display the
avatar and information related to a signature. This allows signatures to
be decoupled from the committer. That being said, allowing arbitary
users to present other peoples commits as theirs is not necessarily
desired therefore we have a trust model whereby signatures from
collaborators are marked trusted, signatures matching the commit line
are marked untrusted and signatures that match a user in the db but not
the committer line are marked unmatched.

The problem with this model is that this conflicts with Github therefore
we need to provide an option to allow users to choose the Github model
should they wish to.

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Adjust locale strings

Signed-off-by: Andrew Thornton <art27@cantab.net>

* as per @6543

Co-authored-by: 6543 <6543@obermui.de>

* Update models/gpg_key.go

* Add migration for repository

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

* paginate results

* fixed deadlock

* prevented breaking change

* updated swagger

* go fmt

* fixed find topic

* go mod tidy

* go mod vendor with go1.13.5

* fixed repo find topics

* fixed unit test

* added Limit method to Engine struct; use engine variable when provided; fixed gitignore

* use ItemsPerPage for default pagesize; fix GetWatchers, getOrgUsersByOrgID and GetStargazers; fix GetAllCommits headers; reverted some changed behaviors

* set Page value on Home route

* improved memory allocations

* fixed response headers

* removed logfiles

* fixed import order

* import order

* improved swagger

* added function to get models.ListOptions from context

* removed pagesize diff on unit test

* fixed imports

* removed unnecessary struct field

* fixed go fmt

* scoped PR

* code improvements

* code improvements

* go mod tidy

* fixed import order

* fixed commit statuses session

* fixed files headers

* fixed headers; added pagination for notifications

* go mod tidy

* go fmt

* removed Private from user search options; added setting.UI.IssuePagingNum as default valeu on repo's issues list

* Apply suggestions from code review

Co-Authored-By: 6543 <6543@obermui.de>
Co-Authored-By: zeripath <art27@cantab.net>

* fixed build error

* CI.restart()

* fixed merge conflicts resolve

* fixed conflicts resolve

* improved FindTrackedTimesOptions.ToOptions() method

* added backwards compatibility on ListReleases request; fixed issue tracked time ToSession

* fixed build error; fixed swagger template

* fixed swagger template

* fixed ListReleases backwards compatibility

* added page to user search route

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: zeripath <art27@cantab.net>

* Add require signed commit for protected branch

* Fix fmt

* Make editor show if they will be signed

* bugfix

* Add basic merge check and better information for CRUD

* linting comment

* Add descriptors to merge signing

* Slight refactor

* Slight improvement to appearances

* Handle Merge API

* manage CRUD API

* Move error to error.go

* Remove fix to delete.go

* prep for merge

* need to tolerate \r\n in message

* check protected branch before trying to load it

* Apply suggestions from code review

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* fix commit-reader

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>

* Move SignMerge to PullRequest

* Add approved signing mode

* As per @guillep2k comment

In investigating #7947 it has become clear that the storage component of go-git repositories needs closing.

This PR adds this Close function and adds the Close functions as necessary.

In TransferOwnership the ctx.Repo.GitRepo is closed if it is open to help prevent the risk of multiple open files.

Fixes #7947

This PR fixes #7598 by providing a configurable way of signing commits across the Gitea instance. Per repository configurability and import/generation of trusted secure keys is not provided by this PR - from a security PoV that's probably impossible to do properly. Similarly web-signing, that is asking the user to sign something, is not implemented - this could be done at a later stage however.

## Features
- [x] If commit.gpgsign is set in .gitconfig sign commits and files created through repofiles. (merges should already have been signed.)
- [x] Verify commits signed with the default gpg as valid
- [x] Signer, Committer and Author can all be different
    - [x] Allow signer to be arbitrarily different - We still require the key to have an activated email on Gitea. A more complete implementation would be to use a keyserver and mark external-or-unactivated with an "unknown" trust level icon.
- [x] Add a signing-key.gpg endpoint to get the default gpg pub key if available
    - Rather than add a fake web-flow user I've added this as an endpoint on /api/v1/signing-key.gpg
    - [x] Try to match the default key with a user on gitea - this is done at verification time
- [x] Make things configurable?
    - app.ini configuration done
    - [x] when checking commits are signed need to check if they're actually verifiable too
- [x] Add documentation

I have decided that adjusting the docker to create a default gpg key is not the correct thing to do and therefore have not implemented this.