[Feature]: Sign commit using GPG when possible

[anton-yurchenko]

In case the user has configured to use a GPG key to sign a commit, version-bump should use that key to sign the commit it creates as well.

[anton-yurchenko]

git config --list has two important settings that must be taken into account:

user.signingkey=XXXXXXXXXXXXXXXX
commit.gpgsign=true

[anton-yurchenko]

It seems that the go-git is unable to load the local git client settings.

[joe-at-startupmedia]

Any updates on this?
https://github.com/go-git/go-git/blob/95afe7e1cdf71c59ee8a71971fac71880020a744/worktree_commit_test.go#L475

Looks like it grabs the contents of the gpg key so I'm not sure how you'd go about providing that configurability in this repo.

Methods to retrieve from local config:
https://github.com/go-git/go-git/blob/95afe7e1cdf71c59ee8a71971fac71880020a744/repository.go#L566

[joe-at-startupmedia]

I tested this and it still doesn't work using repo.ConfigScoped with config.GlobalScope.

The following however does work:

	gitConfig, err := config.LoadConfig(config.GlobalScope)
	log.Info(gitConfig.Raw.Sections.GoString())

	userSection := gitConfig.Raw.Section("user")
	log.Info(userSection)
	log.Info(userSection.Options.Get("signingkey"))

	commitSection := gitConfig.Raw.Section("commit")
	log.Info(commitSection)
	log.Info(commitSection.Options.Get("gpgsign"))

So it seems like the best way to handle this is falling back to config.LoadConfig with the config.GlobalScope when the same key-values grabbed from the Raw sections are non-existent from repo.ConfigScoped with config.GlobalScope.

There is a relevant issue open about this but it seems to be stale:
go-git/go-git#395