feat(ops)!: Sign implementatio based on git

This is based off of git's `gpg-signature.c`

Not happy with all of the extra dependencies we added.  I might want to
consider splitting this out, unsure.

Author: epage

Cargo.lock

@@ -35,6 +35,10 @@ git2 = { version = "0.15", default-features = false }
 log = "0.4"
 itertools = "0.10"
 which = "4"
+bstr = { version = "1.1.0", default-features = false }
+tempfile = "3.3.0"
+shlex = "1.1.0"
+expanduser = "1.2.2"
 
 [dev-dependencies]
 git-fixture = { version = "0.3", features = ["yaml"] }