Add eck security migration

[jfreden]

This PR adds a one-time cleanup task for role mapping duplicates both in cluster state and the .security index. The cleanup task is triggered once, the first time the settings.json is reloaded after this PR has been deployed. The task compares the names of the role mappings in the operator-defined settings.json and the names of the role mappings in the .security index and removes or disables (TBD which one) the one in the .security index. It also adds the name field to the serialization of the role mapping, since the name is needed for the GET Role Mappings API.

Issue

This cleanup is done because there was a bug (fixed here) that caused ECK customers to have the same role mappings with the same names present both in cluster state and the .security index. The effective role mapping is the combination of the .security index mapping and the cluster state one. After the bug fix, if the mapping in cluster state is modified (through setting.json), the .security index will still contain the old mapping and this could lead to unintended behaviour.

Open Questions

• Before this is merged we need to make sure file based settings (settings.json) is re-loaded on every master node restart (draft PR )
• Should we disable or delete roles. The REST API returns disabled roles (with enabled: false) which could be confusing since they're not active during role mapping in the auth/authz flow. Deleting them means users can't recover if the cleanup does something wrong.
• We probably want to separate the mapping serialization change to a separate PR too. Open question is if this should be a new field or just new metadata?

Risks

1. Role mappings might be intended to be defined both in the .security index and the cluster state and will be removed by this PR (minimal since before 8.15 it wasn't possible to this)
2. Role mappings modified in the .security index to workaround the bug fixed here will be removed and all changes might not be reflected in the settings.json role mappings (Only reported by a few customers)
3. This might not trigger for a very long time, increasing the risk of (1) and (2) (mitigated by coupling this with forcing a reload of file settings on master restart)

Dependencies

• link to file setting reload on master restart PR

TODO

• Add new serialization/deserialization to include mapping name
• Add testing
• Figure out snapshot restore flow with new format
• Figure out mixed cluster behaviour