We make remote network hits to get the GPG keys which are quite
unreliable, and apt_key does not support using a proxy properly [1]
so this change installs them from files inside the role.
The implementation here is derived from that which was done in the
galera_server role in I7ac1a5e3a05aa3d0b4fae86c4a325ef147a9a528.
[1] https://github.com/ansible/ansible/issues/31691
Change-Id: Id040de19dbefc820851928c9a3589f20a6b4bd61
Closes-Bug: #1815430
58be4bd5e3