Backend Migration: Migrate PPL Time Series to the backend

[iwysiu]

Prerequisite: #226

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

Similar to #289 and #200