Add multiple redis support

Summary

Omnibus installation could be installed with different external redis instances for different storage types. It seems that this chart currently doesn't support such use case or maybe just haven't this documented https://gitlab.com/gitlab-org/charts/gitlab/tree/master/doc/advanced/external-redis

Current behavior

Only a single Redis can be configured

Expected behavior

Multiple Redis servers can be used to

Versions

• Chart: a1b3da789784b6360f224cc717ab2ae13a749dc4