TUN-9776: Support signing Debian packages with two keys for rollover

* TUN-9776: Support signing Debian packages with two keys for rollover

Debian Trixie doesn't support the SHA-1 algo for GPG keys.

This commit leverages the ability of providing two keys in the reprepro configuration in order to have two signatures in InRelease and Release.gpg files.

This allows users that have the old key to continue fetching the binaries with the old key while allowing us to provide a new key that can be used in Trixie.

Unfortunately current versions of RPM (since 2002) don't support double signing, so we can't apply the same logic for RPM

Closes TUN-9776