test: render helm templates before filtering manifests for debugging
There are a class of Helm errors that are obscured with cryptic
error messages if --show-only is enabled.
To get around this, render all the templates. If that command succeeds,
then add --show-only.
Test Plan: N/A
Reviewers: johann, jordansanders, sidkmenon
Reviewed By: jordansanders
Differential Revision: https://dagster.phacility.com/D8327