Introduce an internal action that the execute policy action delegates to.
This to ensure that the actual policy execution is never executed on the elected master node
or dedicated master nodes. In case the cluster consists out of a single node then
the internal action will attempt to execute on the current/local node.

The actual enrich policy execution is encapsulated in the `EnrichPolicyRunner` class.
This class manages the execution of several API calls, so this itself isn't doing anything heavy.
However the coordination of these api calls (in particular the reindex api call) may involve
some non-neglectable work/overhead and this shouldn't be performed on the elected master
or any other dedicated master node.

Closes elastic#70436

Co-authored-by: Dan Hermann <danhermann@users.noreply.github.com>

…runner_to_non_dedicated_master_node

… response but not release the policy immediately.

Execute get task request with wait_for_completion=true and when that returns release the policy.

…runner_to_non_dedicated_master_node