Advanced Search: Show a warning if `index.blocks.write` is true

This was inspired by https://gitlab.slack.com/archives/C3TMLK465/p1645101835598009 (internal link)

Sometimes Elasticsearch can block writes to an index(es) if there are storage or heap issues.

I believe that we should show a warning in the Advanced Search Admin UI if we detect index.blocks.write or index.blocks.read_only is set to true. It would greatly help with debugging similar issues. This feature could also decrease the number of support cases from self-managed customers.