Add support for Gitaly DNS load balancing in Helm Chart

What does this MR do?

For Gitaly Cluster, we want customers to use client-side load balancing with DNS service discovery (https://docs.gitlab.com/administration/gitaly/praefect/configure/#service-discovery). While this is supported in Omnibus, it was previously not supported for a hybrid Cloud Native GitLab deployment.

Now it can be configured by specifying an address field instead of hostname and port. See https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/grpc_load_balancing.md for more details.

Related issues

• Relates to gitlab-org/gitaly#7000 (closed)
• ZD: https://gitlab.zendesk.com/agent/tickets/681310

Author checklist

1. Set up Gitaly Cluster with Praefect DNS service discovery: https://docs.gitlab.com/administration/gitaly/praefect/configure/, https://docs.gitlab.com/administration/gitaly/praefect/configure/#service-discovery
2. Set global.gitaly.external.address to your Praefect DNS (such as dns://10.128.0.28:8600/praefect.service.consul.:2305).
3. In /srv/gitlab run bundle exec rake gitlab:gitaly:check and ensure the cluster can talk to your Gitaly Cluster nodes.

Required

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

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab chart.