feat: real user as commit author

Previously all commits were authored and committed by

    releaser-pleaser <>

This looked weird when looking at the commit. We now check with the
Forge API for details on the currently authenticated user, and use that
name and email as the commit author. The commit committer stays the same
for now.

In GitHub, the default `$GITHUB_TOKEN` does not allow access to the
required endpoint, so for github the user `github-actions[bot]
<41898282+github-actions[bot]@users.noreply.github.com>` is hardcoded
when the request fails.

internal/forge/forge.go

@@ -17,6 +17,9 @@ type Forge interface {
 
 	GitAuth() transport.AuthMethod
 
+	// CommitAuthor returns the git author used for the release commit. It should be the user whose token is used to talk to the API.
+	CommitAuthor(context.Context) (git.Author, error)
+
 	// LatestTags returns the last stable tag created on the main branch. If there is a more recent pre-release tag,
 	// that is also returned. If no tag is found, it returns nil.
 	LatestTags(context.Context) (git.Releases, error)