This commit removes support for the `application/x-ldjson` Content-Type header as this was only used in the first draft
of the spec and had very little uptake. Additionally, the docs for bulk and msearch have been updated to specifically
call out ndjson and mention that the newline character may be preceded by a carriage return.
Finally, the bulk request handling of the carriage return has been improved to remove this character from the source.
Closes#23025
Add docs to template support for _msearch
Relates to #10885
Relates to #15674
* Reference those docs from the rest api spec for _msearch/template support.
By default the number of searches msearch executes is capped by the number of
nodes multiplied with the default size of the search threadpool. This default can be
overwritten by using the newly added `max_concurrent_searches` parameter.
Before the msearch api would concurrently execute all searches concurrently. If many large
msearch requests would be executed this could lead to some searches being rejected
while other searches in the msearch request would succeed.
The goal of this change is to avoid this exhausting of the search TP.
Closes#17926
This commit brings the benefits of the `count` search type to search requests
that have a `size` of 0:
- a single round-trip to shards (no fetch phase)
- ability to use the query cache
Since `count` now provides no benefits over `query_then_fetch`, it has been
deprecated.
Close#7630