Fix request aborted observable

[nchaulet]

Description

the request.events.aborted$ observable is not working as expected the observable is completed when the request end, (when somebody read request data basically)

This is causing issue in the ingest manager plugin where we try to used that event to limit the concurrency on some routes
https://github.com/nchaulet/kibana/blob/fix-request-aborted-observable/x-pack/plugins/ingest_manager/server/routes/limited_concurrency.ts/#L44-L78

I added a test that reproduce the issue we are experiencing, and one potential solution

Not sure it's the best solution and if we should not rely on a new observable instead?

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 38f2b54

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[joshdover]

In my testing, this change does appear to be correct. Right now the aborted$ observable will complete prior to the response being sent back, which may cause us to lose aborted events. This appears to only happen on POST requests that define body validation because the end event is being fired when the request body is read. On GET requests, the aborted$ Observable does not complete until the connection is closed.

I propose we bundle this fix with the addition of a real completed$ event which will emit whenever the request is either aborted, or a response has been sent back to the client. Here is a PR: #73898

[nchaulet]

Closed in favor of #73898