Use BucketIndexBlocksFinder instead of BucketScanBlocksFinder

[leizor]

What this PR does

The use of BucketScanBlocksFinder was supposed to be removed in #6673 but its counterpart BucketIndexBlocksFinder was accidentally removed instead.

This PR also removes references to the old bucket scan option from the docs.

This reverses that.

Which issue(s) this PR fixes or relates to

#6670

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• about-versioning.md updated with experimental features.

[leizor]

This is less straightforward than I expected; marking as a draft for now while I figure out the failing integration tests.

[dimitarvdimitrov]

That's great!

But I think we can do better. Can you also remove the alert and its runbook

mimir/operations/mimir-mixin/alerts/blocks.libsonnet

Lines 186 to 201 in 7d9b3d4

	{
	// Alert if the querier is not successfully scanning the bucket.
	alert: $.alertName('QuerierHasNotScanTheBucket'),
	'for': '5m',
	expr: |||
	(time() - cortex_querier_blocks_last_successful_scan_timestamp_seconds > 60 * 30)
	and
	cortex_querier_blocks_last_successful_scan_timestamp_seconds > 0
	|||,
	labels: {
	severity: 'critical',
	},
	annotations: {
	message: '%(product)s Querier %(alert_instance_variable)s in %(alert_aggregation_variables)s has not successfully scanned the bucket since {{ $value | humanizeDuration }}.' % $._config,
	},
	},

After doing that you should probably run make build-mixin build-helm-tests and commit the diff

[leizor]

@dimitarvdimitrov Good call, done!

[dimitarvdimitrov]

LGTM, thanks so much for doing this

[leizor]

Thanks for the reviews!

[grafanabot]

The backport to r267 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-6779-to-r267 origin/r267
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x ff8a70aee6d187113d0f2b18b75144a4bee5091d
# Push it to GitHub
git push --set-upstream origin backport-6779-to-r267
git switch main
# Remove the local backport branch
git branch -D backport-6779-to-r267

Then, create a pull request where the base branch is r267 and the compare/head branch is backport-6779-to-r267.

[pr00se]

This didn't need to be backported to r267 (the changelog entry was added in #6808)