Accept multiple bind addresses in Redis config

What does this MR do?

As specified in https://redis.io/docs/management/config-file/, Redis can bind to multiple addresses with a space-separated field. Previously attempting to do this without setting gitlab_rails['redis_host'] would fail because a URI could not be built with a space in the hostname.

This commit now splits the string with the space and picks the first address as the default Redis host.

How to validate locally

1. Configure /etc/gitlab/gitlab.rb:

redis['bind'] = '127.0.0.1 172.17.0.3' # Substitute the second address with some valid address
redis['port'] = 6379

2. Run gitlab-ctl reconfigure.
3. Ensure redis still works: gitlab-ctl tail redis
4. Ensure GitLab still works.
5. Ensure gitlab-redis-cli connects successfully.

Related issues

Relates to #8465 (closed)

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.