[SLO] Add SLO transform stats to the kibana diagnostic tool

[mgiota]

🍒 Summary

We can automatically get from the Kibana diagnostic tool any key information we want without asking for specific APIs or queries to be run by the customers. We need to enhance the tool to pull from the API we specify. This would allow Support Engineers or Developers who work SDHs or Cases to get the API output without asking the customer.

We could include the SLO transform stats in the Kibana diagnositc tool.

✔️ Acceptance criteria

• add _transform/slo-*/_stats api call to the diagnostic tool
• is there any other useful information we would like to automatically send to the diagnostic tool apart from transform stats? _health api could be a good candidate, but it is a POST request and requires a list of SLOs

Note @lucabelluccini is kibana-rest.yml the proper place for our use case, or shall we add the api call to elastic-rest.yml, similar to the transform stats that were added recently as part of this PR

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)