Warn user when freeze action will be removed from an ILM policy

[cjcenizal]

#116160 removes the freeze action from the ILM UI, and also silently removes the freeze action from any policy saved through this UI.

Ideally, users will remove the freeze action from their ILM policies as part of the upgrade preparation process, as noted in elastic/elasticsearch#70192 (comment).

However, some users might still keep the freeze action on their policies during the upgrade. In this case, the ILM UI should notify the user that the freeze action is now a no-op and will be removed from the policy. It should also offer the user guidance on what to do instead.

The ES issue that deprecates this action (elastic/elasticsearch#70192), identifies 7.7 improvements in heap utilization and the new frozen tier as superior alternatives to the freeze action. Ideally, the ILM UI will direct the user to documentation on how to migrate to these alternatives.

This issue is blocked on the outcome of the discussion started by elastic/elasticsearch#70192 (comment).

[elasticmachine]

Pinging @elastic/kibana-stack-management (Team:Stack Management)

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)