[FEATURE] Establish periodic polling of extensions to verify connectivity

[dbwiddis]

Is your feature request related to a problem?

Part of #356

What solution would you like?

Establish periodic polling of extensions to verify connectivity (both ways)

• Add retry on startup (exponential fallback)
• Allow user to configure auto-restart

[saratvemulapalli]

Some thoughts here: OpenSearch nodes uses transport protocol and when a node dies, it gets notified instantly. We could do something similar for extensions.

[dbwiddis]

Some thoughts here: OpenSearch nodes uses transport protocol and when a node dies, it gets notified instantly. We could do something similar for extensions.

Definitely a good add-on, but this also needs to handle the use case of OpenSearch starting up, and the extension not being (yet) available (i.e., no connection exists to "die").