Make ActionCable Redis settings use default Redis Sentinel password

What does this MR do?

Suppose you have this config:

gitlab_rails['redis_sentinels'] = [
  {"host"=>"gitlabtest-cluster-redis-01", "port"=>26379},
  {"host"=>"gitlabtest-cluster-redis-02", "port"=>26379},
  {"host"=>"gitlabtest-cluster-redis-03", "port"=>26379}
]
gitlab_rails['redis_sentinels_password'] = "some password"
redis['enable'] = false
redis['master_name'] = "gitlab-redis"
redis['master_password'] = "some password"

Previously ActionCable Redis settings would only look for gitlab_rails['redis_actioncable_sentinels_password'] and did not fall back to gitlab_rails['redis_sentinels_password'].

Related issues

Relates to #8728 (closed)

Checklist

See Definition of done.

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Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• Latest Merge Result pipeline is green.
• When ready for review, MR is labeled workflowready for review per the Distribution MR workflow.

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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
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added devopssystems groupdistribution sectioncore platform labels

assigned to @stanhu

marked the checklist item MR title and description are up to date, accurate, and descriptive. as completed

marked the checklist item MR targeting the appropriate branch. as completed

changed milestone to %17.5

added workflowready for review label

mentioned in issue #8728 (closed)

marked the checklist item When ready for review, MR is labeled workflowready for review per the Distribution MR workflow. as completed

added typebug label

	1 Warning
	Please add a merge request subtype to this merge request.

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Reviewer	Maintainer
@brodock (UTC+1, 8 hours ahead of @stanhu)	@apatterson2 (UTC-6, 1 hour ahead of @stanhu)

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Generated by Danger

requested review from @jondoveston

E2E Test Result Summary

allure-report-publisher generated test report!

qa-subset-test: test report for 448d9d3c

expand test summary

+---------------------------------------------------------------------+
|                           suites summary                            |
+----------------+--------+--------+---------+-------+-------+--------+
|                | passed | failed | skipped | flaky | total | result |
+----------------+--------+--------+---------+-------+-------+--------+
| Govern         | 48     | 0      | 2       | 0     | 50    | ✅     |
| Create         | 46     | 0      | 20      | 0     | 66    | ✅     |
| Plan           | 19     | 0      | 0       | 0     | 19    | ✅     |
| Monitor        | 8      | 0      | 1       | 0     | 9     | ✅     |
| Release        | 1      | 0      | 0       | 0     | 1     | ✅     |
| Systems        | 6      | 0      | 1       | 0     | 7     | ✅     |
| Package        | 10     | 0      | 4       | 0     | 14    | ✅     |
| Data Stores    | 11     | 0      | 0       | 0     | 11    | ✅     |
| Verify         | 4      | 0      | 1       | 0     | 5     | ✅     |
| GitLab Metrics | 2      | 0      | 1       | 0     | 3     | ✅     |
| Manage         | 2      | 0      | 0       | 0     | 2     | ✅     |
| Configure      | 1      | 0      | 0       | 0     | 1     | ✅     |
+----------------+--------+--------+---------+-------+-------+--------+
| Total          | 158    | 0      | 30      | 0     | 188   | ✅     |
+----------------+--------+--------+---------+-------+-------+--------+

requested review from @balasankarc and removed review request for @jondoveston

added group::distributionbuild label

added Category:Build label

@stanhu What happens if a user have one set of sentinels with password for Redis and another set without password for ActionCable? Should we gate this on whether Gitlab['gitlab_rails']['redis_actioncable_sentinels'] is empty or not (which should mean that actioncable uses the same sentinels as Redis)?

As @balasankarc & @rmarshall are currently OOO, asking @apatterson2 to review.

requested review from @apatterson2 and removed review request for @balasankarc

added workflowin review label and removed workflowready for review label