Replace usage of /elasticsearch/_msearch endpoint in Index Pattern Management UI

[joshdover]

In order to unblock removing legacy plugin support (#71927) we need to remove all usages of the /elasticsearch/_msearch endpoint. This can be replaced with a specific endpoint in the index_pattern_management plugin that provides only the needed functionality for the frontend.

kibana/src/plugins/index_pattern_management/public/components/field_editor/lib/validate_script.ts

Line 65 in 4eb455d

const esResp = await http.fetch('/elasticsearch/_msearch', { method: 'POST', body });

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[lukasolson]

Just an FYI this isn't the only place the endpoint is used, it's also used if you have the courier:batchSearches setting turned on. (See #54147 and #55140.)

[joshdover]

@lukasolson Just saw your comment here. Are we going to need to keep this endpoint until 8.0 in order to not break that feature? Is that a feature we must keep around until 8?

If so, maybe the best course of action here is for the Platform team to migrate this endpoint out of legacy and mark it as deprecated.

[lukeelmers]

Are we going to need to keep this endpoint until 8.0 in order to not break that feature? Is that a feature we must keep around until 8?

Yes, I believe the plan is to keep that setting around until 8.0

I'm currently working on an /internal/msearch endpoint which has some extra handling which would allow us to close this issue and #55139 at the same time.

[pgayvallet]

@lukeelmers I see #75943 unfortunately did not address this issue. This is still planned for 7.10, right?

[joshdover]

pinging @lukasolson since Elmers is out ⬆

[lukasolson]

Yes, I believe this is still being targeted for 7.10.

[lukeelmers]

I'm actively working on this now, expecting to have a PR ready soon.

[lukeelmers]

PR is up: #77564