Migrate datanode CA to cluster config service, refactor handling

[todvora]

• Migrate the CA keystore from its own collection to cluster config service. It significantly simplifies handling, provides support for encrypted values deserialization and keeps the distributed nature of the CA.
• Adapt CaKeystore and services around this abstraction to the change
• Remove unused services and classes
• Simplify and minimize passwords handling for CA
• Remove unnecessary dependency injection where it doesn't make sense

Motivation and Context

Overall PKI infrastracture in the datanode and server code.

How Has This Been Tested?

Existing unit and integration tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.