[8.0 only] Remove xpack.task_manager.index setting

[mikecote]

See #101964.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[chrisronline]

Reopening as we had to revert due to #108111 (comment)

[kobelb]

Blocked on https://github.com/elastic/observability-test-environments/issues/915

[gmmorris]

Sounds like @cachedout is due to send out an email blast in Observability today with instruction on how they can move away from legacy multitenancy.

This should mean that this issue is unblocked, but I'm not sure how much time we'd like to give the O11y team to move their dev envs over before we remove the config on Main.

Watch this space ;)

[cachedout]

@gmmorris Thanks for the ping. As you rightly point out, we'll still need a bit of time even after sending out the notice in order for Obs devs to try it out, answer questions that they might have, and fix any urgent issues that come up.

I wouldn't consider this issue unblocked just yet, but we're getting quite close. We'll keep you posted on progress, of course. :)

[gmmorris]

Thanks @cachedout , we'll likely have to do it once we go past 7.16FF as we only have a week after that until 8.0FF.
Is that doable in your opinion?

[cachedout]

@gmmorris Yes, barring anything unforeseen that timing should work for us. (cc: @kuisathaverat )

[chrisronline]

FWIW, I recreated the PR in draft mode (#114558) and ready to review it once we get the green light from @cachedout 9

[cachedout]

@chrisronline I think you can tie this to the date that @kobelb recently set (Oct 21) for the kibana.index setting. Not sure if you need to check him with him first or not, but this is a 👍 from our end.

cc: @kuisathaverat

[chrisronline]

@cachedout Thanks for the note! I synced with @kobelb and we're all set to merge this on Oct 21!

[chrisronline]

Update here. The PR for this work will not be merged until EOD 10/25 (5pm ET)