[FEATURE] Cache the cluster state request for query insights reader

Is your feature request related to a problem?

Each time we invoke the reader, we make a request to the cluster state api to fetch all available indices. There are some overhead with this approach.

What solution would you like?

Ideally we should cache the index names and update the cache whenever the cluster state is changed

What alternatives have you considered?

A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?

Add any other context or screenshots about the feature request here.