Update CI workflow to adapt to new project structure

[avaerian]

Because the project structure is changing, the CI workflow needs to adapt to the updated build process.

Proposed changes:

• 2 workflows: base-plugin and full-plugin
  • base-plugin compiles and tests only the main module
  • base-plugin will test main module. If passing, compile and package uber jar. Else, fail.
  • full-plugin compiles and tests all modules (compiles runnable plugin)
  • base-plugin runs when changes are pushed to the development or feature/* branches
  • full-plugin runs when changes are pushed to the master branch
• For better Gradle build times, cache Gradle build results

[avaerian]

Things to do:

• Unit testing for shadowJar in workflow
• Figure out Gradle caching (as of right now it's read-only?)

Later I want to investigate having the workflow run the jar in a docker container for integration testing, but that's for later.