Improve validation script

[anderseknert]

Improvements include:

• Accept template(s) via arguments rather than hardcoded
• Can send a single resource to OPA or all from directory
• Add --test flag to run integration tests (same as before)
• Without --test flag, just print the response from OPA, allowing rapid iteration of policy and template development.
• Accept JSON templates as well as YAML.
• Fixed some strict failures due to unused imports, not sure how they passed the CI tests before

Fixed #20 and #21

Signed-off-by: Anders Eknert anders@eknert.com