Implement OpenPGP using librpm API

[jrohel]

Implements the original librepo OpenPGP API using librpm API instead of GpgMe. It implements its own keyring for public keys. Each key with its subkeys is stored in its own file. The original GpgMe based implementation was moved to the "gpg_gpgme.c" file. So it is still present and can be activated by the USE_GPGME option in "CMakeList.txt". This PR leaves the original GpgMe implementation enabled by default in CMakeList.txt. In the .spec file it switches to the librpm API for Fedora >= 39.

Requirement: A new rpm library is needed that supports OpenPGP ASCII Armored signature parsing. Tested with sequoia based rpm OpenPGP backend.

Missing (requires support in the rpm library):

• Setting the can_sign property. It now always returns TRUE.
• Fingerprint for subkeys. An empty string is now returned.
• Return all user IDs. Now only one returns

Notes: In the Python tests, pgp tests that should succeed were disabled. This is because librepo lacks a Python API for working with OpenGPG keys. The Python tests manipulate the keyring directly using GpgMe. Of course, this only works if the librepo library uses the original GpgMe backend.

[kontura]

I think the CI should be fixed by a rebase.