[Doc] Add documentation for <LockOnMount> and <WithLocks> headless components

[jonathanarnault]

Problem

<LockOnMount> and <WithLocks> are not documented

Solution

Document the components in ra-core documentation and add setting page for Realtime features

How To Test

make doc-headless, the go to

• http://localhost:4321/ra-core/realtimefeatures/
• http://localhost:4321/ra-core/lockonmount/
• http://localhost:4321/ra-core/withlocks/

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

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