Background

1. The EnhancedKeyStoreLoader uses node self names from the AddressBook to compose file names that contain keys for that node.
2. As the Platform migrates from using the AddressBook to using the Roster, custom node names are getting replaced with generated names of form node<id+1>.
3. Per @iwsimon , in production all nodes already use self names of this format, and we already use .pem keys via the EnhancedKeyStoreLoader in prod.
4. In Regenerate keys and update node names for tests #15789 , we've also updated Platform tests that used custom node names and replaced legacy .pfx keys with new .pem keys.

Acceptance criteria

1. The EnhancedKeyStoreLoader should stop using custom self names, and should enforce using names of form node<id+1> for the purpose of loading keys.
2. Unit tests for the EnhancedKeyStoreLoader should be updated to follow this changes, which may require regenerating some legacy keys to use the new names. Alternatively, support for the legacy keys should be removed from the code-base altogether.

Notes

1. There may or may not be additional impact to any of the testing environments (e.g. testnet, perfnet) as well as testing frameworks (JRS, Solo, etc.) that may require extra changes or coordination (with devops etc.) We'll only be able to discover them once the main change from the Acceptance criteria is implemented and merged.