Leftovers of PR #4771

[dmartinol]

This issue is defined to track the leftovers of #4771 that must be closed before the next release:

• infra/feast-operator/config/samples/v1alpha1_featurestore_db_persistence.yaml: add sample secret link
• Can you add simple tests for invalid store type for each of the feast service? link
• Test overriding secret keys link
• Fix examples in the decription (wrong usage of secretKeyName)
• Use required fields in CRD type link, other
• Describe CRD types link
• Unit test incorrect types link

@tmihalac @tchughesiv