sql: include sql fingerprint id in workload_index_recs built-in

[kyle-a-wong]

Is your feature request related to a problem? Please describe.
The workload_index_rec built-in returns a set of index recommendations, but it is not clear how these index recommendations will impact the workload or which fingerprints will benefit from them.

Describe the solution you'd like
The workload_index_rec built-in should include the fingerprint ids of the queries that will benefit from the index recommendations. Currently, the built-in returns a set of index recommendations (as strings). This could be updated to be a jsonb type with the following structure:

{
  "index_recommendation" : string,
  "impacted_fingerprint_ids" : []string
}

Jira issue: CRDB-48091