Support commit signing

[paveldvoinos]

Support signed commits by importing a private key from secrets into the gpg keystore on the fly.

[andrii-bodnar]

@paveldvoinos thanks a lot for your contribution!

[andrii-bodnar]

Hi @paveldvoinos!

It's been a long time :)

but could you please assist with the error related to this commits signing feature?

FOUND PRIVATE KEY, WILL SETUP GPG KEYSTORE
gpg: directory '/github/home/.gnupg' created
gpg: keybox '/github/home/.gnupg/pubring.kbx' created
gpg: /github/home/.gnupg/trustdb.gpg: trustdb created
gpg: key ***: public key "***" imported
gpg: key ***: error sending to agent: Not a tty
gpg: key ***: error sending to agent: Not a tty
gpg: error reading 'private.key': Not a tty
gpg: import from 'private.key' failed: Not a tty