[Firehose] Secret resource creation should be conditional

[rajat404]

Currently as per the secret template, the secret and secret mount resources are created for each helm release even if no secrets are provided in the values file.

The secret resource creation should be conditional on the presence of non-empty values for those fields in the values file.

This can be done by adding an if condition block in secrets.yaml for each - secret and secret mount.

I'd be happy to raise a PR for this, if the maintainers agree with the proposed change.