Support for OPA Conftest

[jdoylei]

It would be great if the opa-idea-plugin could also support running the separate Conftest utility that scans/tests projects consisting of configuration data (like Kubernetes resource manifests).

What would you like to be added

• Ability to trigger Conftest with one or more selected files in the current IntelliJ project as its input "configuration files" to be tested
• Ability to load Conftest's "junit" output ( XML report file) and render in IntelliJ's Test Runner tab, to show failed tests etc.
• Ability to configure the Conftest run to include a pre-processing step on the configuration files before they're passed to Conftest, like running Kustomize on them

Why is this needed

• Conftest is a great utility, but the best integration you can set up currently is to run it as a generic shell script command in IntelliJ's terminal. Having it integrate automatically with the Test Runner tab would make it more developer-friendly and easier to include in the workflow of updating configuration files.