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.
* Change tests to make it possible to run TestGit with 1.7.2
* Make merge run on 1.7.2
* Fix tracking and staging branch name problem
* Ensure that git 1.7.2 works on tests
* ensure that there is no chance for conflicts
* Fix-up missing merge issues
* Final rm
* Ensure LFS filters run on the tests
* Do not sign commits from temp repo
* Restore tracking fetch change
* Apply suggestions from code review
* Update modules/repofiles/temp_repo.go
* extract actions on new pull request from models to pulls service
* improve code
* move code.gitea.io/gitea/modules/pull to code.gitea.io/gitea/services/pull
* fix fmt
* Rename pulls.go to pull.go
