[CCR] Introduce leader index setting for follow index

[martijnvg]

Associate the uuid of the leader index in the follow index's index settings.
The follow index api should fail if this index setting in the follow index and
should check if the uuid in the follow index matches with uuid of the leader index.

This validation will prevent a follow index from following an incompatible leader index.

The create and follow api should introduce this setting when it creates the follow index.

Relates to #30086

[elasticmachine]

Pinging @elastic/es-distributed