EQL: enable CPS

[luigidellaquila]

Add CPS settings both to EQL action and to inner field_caps invocation

PIT is not ready for it yet, it will be managed with a follow-up PR

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Hi @luigidellaquila, I've created a changelog YAML for you.

[luigidellaquila]

@piergm It seems to work fine, but I have a doubt: I changed indicesOptions for the field_caps call (fan-out), but not for the subsequent _search calls. Should I also do it in that case?

This is where I prepare the search requests: https://github.com/elastic/elasticsearch/blob/main/x-pack/plugin/eql/src/main/java/org/elasticsearch/xpack/eql/execution/search/RuntimeUtils.java#L189-L196

[piergm]

@luigidellaquila I have to take a deeper look, but I think we should do the same as we do for the field caps call.
My theory on why it's currently working is because both PIT (so MRT=false) and _search with MRT=true are not CPS enabled.