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.

* improve integration tests

* fix Makefile

* improve makefile and integration docs

resolves git conflicts from #3896 (credit to @belak, in case github doesn't keep original author during squash)

Co-Authored-By: Matti Ranta <techknowlogick@gitea.io>

* Rename BaseLogger to WriterLogger to help the creation of other providers

* Don't export ColorBytes and ResetBytes from ColoredValues

* Make integration tests only print logs if they fail

* check can color before coloring

* I always forget about MSSQL

* Oh and use LEVEL in sqlite.ini

* Make the test logger log at info - as it means you see the router

* Remove empty expected changes

* Make the migrations quieter too

* Don't display SQL on error - it can be looked at in the file logs if necessary

* Fix skip when using onGiteaRun

* Create log mailer for testing email settings

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

* Switch on the log mailer for the integration tests

This ensures that the sending mail process works

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

* rename the from user for mysql/mssql

* rename log sender to dummy sender

* update the integration tests

* Added test environment for m$sql

* Added template for test environment for m$sql

* Fix password

* Fix password (again)

* Fix password (again again)

* Fix db

* Ci trigger (Looking at you drone....)

* Ci trigger (Looking at you drone....)

* Ci trigger (Looking at you drone....)

* Ci trigger (Looking at you drone....)

* Create master database for mssql integration tests

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Create database only if master do not exist

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Fix mssql integration tests by using custom database "gitea"

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Moved defer

* bump xorm

* updated xorm

* Fixed build