[FEATURE] Add metrics for index policy failed

[Jakob3xD]

Idea

I would like to have a metric to see if a policy is in failed state for and index.
GET _plugins/_ism/explain returns some information that can be used as labels.

Example

Value should 1 if it failed and 0 if it is running.

opensearch_index_policy_failed{policy_id="policy-1",state="init_state",action="rollover"} 0

[lukas-vlcek]

That is an interesting idea! Coincidentally I have been working with ISMs recently, I think this metric can be very useful.