Backend: Remove _doc from sort array in query building, Remove limit from response processing, Prepare release v2.13.1

[fridgepoet]

What this PR does / why we need it:
This PR addresses any difference between the frontend and backend query building and response processing to Grafana data frames for Lucene logs.

The only change in this PR is in bold text.

Difference list:
Query building to OpenSearch:

• Backend has "docvalue_fields":["timestamp"]. Frontend code does not add this value, but I am reluctant to remove it as it seems like some kind of optimization (1, 2). It does not seem to negatively affect the behavior. For what it's worth Elasticsearch also has this in the query input.
• Frontend has an extra empty nested "aggs" in the "aggs" object which is not present in the backend. It doesn't seem to serve a purpose, so not adding it to the backend. This is not present in Elasticsearch in an equivalent query.
• Backend code has an extra object "fields" with timeField "format": "strict_date_optional_time_nanos", which was a fix based on Elasticsearch: Fix processing of logs with not-recognized time format grafana#67767. It was included in Add raw_data query support to backend #203.
• Backend's sort object is an array which was changed from a single object as it is in the frontend in Change query sort to respect sort order #211
• Backend's sort has {"_doc":{"order":"desc"}} which is not present in the frontend. This came from the equivalent backend migration PR of Elasticsearch, but I don't see evidence of _doc anymore in the latest OpenSearch documentation. In any case since this is not present in the frontend, this was removed.

Grafana data frame response:

• Backend has an extra "limit" object which is not in frontend. This came from the equivalent backend migration PR of Elasticsearch, but the UI includes a "limit" option which OpenSearch does not currently have. This was removed.

Which issue(s) this PR fixes:

Contributes to #199

Special notes for reviewers:
Testing was done locally by including the changes from this branch: https://github.com/grafana/opensearch-datasource/tree/backend-flow
This redirects all Lucene queries to the backend (not just from the Explore view).