Fix reconfigure failing when Sentinel TLS is only enabled

What does this MR do?

If the unencrypted Sentinel port is disabled and only TLS enabled, gitlab-ctl reconfigure previously failed because it attempted to talk to port 0, which is an invalid port.

This commit fixes this problem by switching to TLS if is the only option. In addition, server and client certificates need to be provided to redis-cli if required.

NOTE: GitLab currently does not function if Sentinel TLS is only enabled; this only fixes the gitlab-ctl reconfigure.

Related issues

Relates to #6627 (closed)

How to validate locally

1. As described in https://redis.io/docs/management/security/encryption, create TLS certs:

cd /tmp
curl -L -O https://raw.githubusercontent.com/redis/redis/7.2/utils/gen-test-certs.sh
# This will generate certs in /tmp/tests/tls
bash ./gen-test-certs.sh

2. Copy these certs into the right locations:

cd tests/tls
sudo chmod a+r *.crt
sudo chmod 0600 *.key
sudo cp ca.crt /etc/gitlab/trusted-certs
sudo cp redis.key redis.crt /etc/gitlab/ssl
sudo chown gitlab-redis /etc/gitlab/ssl/redis.key

3. In /etc/gitlab/gitlab.rb add:

sentinel['enable'] = true 
sentinel['bind'] = '0.0.0.0'
sentinel['port'] = 0
sentinel['tls_port'] = 26379
sentinel['tls_cert_file'] = '/etc/gitlab/ssl/redis.crt'
sentinel['tls_key_file'] = '/etc/gitlab/ssl/redis.key'
sentinel['tls_replication'] = 'yes'
sentinel['tls_auth_clients'] = 'yes'
sentinel['bind'] = '0.0.0.0'

4. Run gitlab-ctl reconfigure.

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

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 "~workflow::ready for review" per the Distribution MR workflow.

For GitLab team members

If you don't have access to this, the reviewer should trigger these jobs for you during the review process.

• The manual Trigger:ee-package jobs have a green pipeline running against latest commit.
• If config/software or config/patches directories are changed, make sure the build-package-on-all-os job within the Trigger:ee-package downstream pipeline succeeded.
• If you are changing anything SSL related, then the Trigger:package:fips manual job within the Trigger:ee-package downstream pipeline must succeed.
• If CI configuration is changed, the branch must be pushed to dev.gitlab.org to confirm regular branch builds aren't broken.

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
• Documentation created/updated.
• Tests added.
• Integration tests added to GitLab QA.
• Equivalent MR/issue for the GitLab Chart opened.
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.