Backend: Implement Lucene raw_data queries in the backend

[idastambuk]

Note: Blocked by #196

Currently, Lucene raw_data queries are processed as Lucene logs (

opensearch-datasource/src/OpenSearchResponse.ts

Line 447 in ace6755

processResponseToDataFrames(

) (frontend). This flow needs to be compared and migrated to the backend.
On the backend, raw_data is processed in the backend in getTimeSeries but is incomplete. It will need to be separated: See this ElasticSearch refactor PR and grafana/grafana#59741

Some general guidelines are:

• Create visualization to compare between frontend and backend flows, preferably in a shared Cloud dashboard e.g. clouddatasources.grafana.net
• Unit tests in the frontend should be copied or updated in the backend to assert the same behavior and add unit tests when there are none.
  • Check Elasticsearch repo for related tests – helpful when there are no OpenSearch tests in the frontend or backend
• We should match OpenSearch's backend behavior to the current frontend behavior, but be aware it may not always make sense. Elasticsearch's current behavior is also another resource for how OpenSearch should behave.
  • Let's be pragmatic about this – our foremost goal is the migration of OpenSearch's frontend behavior. We can aim for some Elasticsearch feature parity, but only within reason.
• Often there is a PR in the Elasticsearch backend data source migration Elasticsearch: Convert the datasource to be a backend datasource grafana#54011 which is 75% of what OpenSearch will need
• Migrate or implement: i.e. make any changes to code in backend
• Use the dashboard created above to compare visualization results (data frame comparison)
  • Can also inspect data frame on a more detailed basis