Covert To Gradle

[zromano]

This MR converts our build system from Maven to Gradle.

The advantages of doing this are:

• Gradle has more performant builds
• Gradle is much easier to read and understand
• Gradle tasks are more easily modifiable
• Most importantly: The team likes Gradle 😄

Things I know are left to do:

• [x] Figure out how to make the docs
• [x] Update the .gitignore for Gradle
• [x] Make jacoco work for code coverage.   - It's mostly wired in, I just wasn't sure if we include IT tests and SDK tests in the coverage or not? [Note: they are not included in coverage. Pipeline only runs unit tests]
• [x] Make sure the IT tests work (should be able to run ./gradlew clean integrationTest
  • Note: They work, but LoggingIT and OAuthFlowImplIT are currently broken due to my previous MR
  • [x] Make sure the SDK tests work (should be able to run ./gradlew clean sdkTest
• [x] Ensure everything else in the POM is covered. Make sure we support anything the maven plugins were doing
  • [x] Need to sign artifacts
  • [x] Add details from the POM's developer tag
  • [x] Check if we need nexus plugin
  • This is for if we want to deploy to a private Nexus repo for SNAPSHOT deploys. We do not currently do this
  • [x] Check what the maven-shade-plugin does
  • Used for building fat jars (https://stackoverflow.com/a/13620420). We never use this currently
  • [x] Check what license-maven-plugin does
  • Updates the license.txt and the headers of files. We don't currently use so we can update later
  • [x] Determine how .maven.xml works
  • This isn't used. It used to be used for the pipeline when we used Travis CI. It was just never cleaned up.
• [x] Update our pipeline to use gradle commands
  • [x] Builds
  • [x] Publish Docs
  • [x] Releases
• [x] Remove the POM and other maven related files
• [x] Update docs to refer to Gradle instead of Maven

[zromano]

Looks like I've managed to commit from both of my Github accounts 🤦