Update namespaces to be consistent across manifests

What does this MR do?

I noticed that some resources for the GitLab Rubber (the deployment, secret, and configmap) will be installed to the default namespace even when specifying the Helm namespace.

This merge request resolves that issue, as well as makes the namespace definition consistent across the manifests, as some did not include the default .Values.runners.namespace and some did (although I noticed that flag is now deprecated).

Why was this MR needed?

GitLab Runner resources were being installed into the default namespace while all other resources from the main chart were being installed into a specified namespace.

What's the best way to test this MR?

# Test with default namespace
helm template gitlab . --values values.yaml

# Test with custom namespace
helm template gitlab . --values values.yaml --namespace=gitlab-runner

What are the relevant issue numbers?

N/A