internal/rosa: wrapper around git helper

This results in much cleaner call site for the majority of use cases.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/git.go

@@ -114,3 +114,8 @@ git \
 rm -rf /work/.git
 `, resolvconf())
 }
+
+// newTagRemote is a helper around NewViaGit for a tag on a git remote.
+func (t Toolchain) newTagRemote(url, tag, checksum string) pkg.Artifact {
+	return t.NewViaGit(url, "refs/tags/"+tag, mustDecode(checksum))
+}