Add support for GPG key in scylladb keyring file

[tarzanek]

fixes #279

[tarzanek]

tested with 2023 and old 2022.2

[tarzanek]

fwiw I tested on Ubuntu 20 and no leftovers of https://github.com/scylladb/scylladb/issues/14965 anywhere with this approach

[vladzcloudius]

Looks good. Merging. @ebenzecri can you, please, test this with some latest SW versions that require these keys in a Training.

Please, test with U20 and U22.04. Criteria for success: 1) Installation works as expected. 2) There is not dirmngr running after the installation: sudo ps -elf | grep dirm - should be empty.

[ebenzecri]

Versions that I've set for testing this feature:

• ScyllaDB Enterprise 2022.2.13 (specific keyring file is not required)
• Scylla Manager 3.2 (specific keyring file required)

Ubuntu 20.04

• "Create cluster" job finished successfully (http://localhost:8081/job/Ops/job/Create_cluster/247/console).
• scylla-manager-client and scylla-manager-server installed on "manager": 3.2.0-0.20230815.9db309c5
• scylla-manager-agent installed on all nodes: 3.2.0-0.20230815.9db309c5
• sudo ps -elf | grep dirm output: Empty

Ubuntu 22.04

• "Create cluster" job finished successfully (http://localhost:8081/job/Ops/job/Create_cluster/248/console).
• scylla-manager-client and scylla-manager-server installed on "manager": 3.2.0-0.20230815.9db309c5
• scylla-manager-agent installed on all nodes: 3.2.0-0.20230815.9db309c5
• sudo ps -elf | grep dirm output: Empty

It seems it's working as expected. I'll upgrade all 2022.2 clusters to Scylla Manager 3.2 then. Thanks!