Remove dependency on key metadata files of KMS plugins

[amartinezfayo]

As part of the goal of removing server dependency on on-disk data, we need the KMS plugins to avoid having to store a file that stores an auto-generated server ID, that's used to keep track of the keys managed by the plugin.
This file is referenced as the key metadata file by the KMS plugins.

[keeganwitt]

This ticket said metadata files. Does that mean AWS's key_policy_file and GCP's service_account_file and key_policy_file don't need a way to be avoided?

[amartinezfayo]

None of those configs are a required configuration, so they haven't been targeted as a primary goal to remove the dependency on disk storage for the plugins. If those configs are a problem in your use case, I suggest to explore solutions separately.

[keeganwitt]

None of those configs are a required configuration, so they haven't been targeted as a primary goal to remove the dependency on disk storage for the plugins. If those configs are a problem in your use case, I suggest to explore solutions separately.

They're not, just confirming I understood the requirements.

[keeganwitt]

If there are any character restrictions for the ID, we should document those too.