Show GPG signature indicator in Commits

**Is your feature request related to a problem? Please describe.**
`git log` allows viewing GPG signatures with the `--show-signature` flag. Currently, there is no way (I know of) to see these in Lazygit.

**Describe the solution you'd like**
Provide a configuration option for displaying them:
1. As little indicator in the Commits panel.
2. With information like git `git log --show-signature` does in Log and Patch panels.

**Additional context**
`git log -1 --show-signature`:
```
commit ecd0a96cdaef71c29655aa9b58ca414bf5efea1e (HEAD -> main)
gpg: Signature made Mon Apr 25 17:30:23 2022 CEST
gpg: using RSA key DAC501BB46861CC3D064BA3B50027A3368AA398E
gpg: Good signature from "Benedikt Müller (d12bb) " [ultimate]
Author: Benedikt Müller
Date: Mon Apr 25 17:29:35 2022 +0200

commit message

```