Checkstyle and PMD report parsing

[kloessst]

Motivation and Context

This PR extends the parsing functionality for static code analysis reports.

Description

• Add XOM for parsing
• Add PMD parsing
• Add Checkstyle parsing
• Switch to parsing of the more verbose spotbugsXml, as it contains a proper source path. Opened an issue to add this information to the xdoc report but this might take a while.
• Rename classname to filePath
• Rename type to rule
• Add PR template

Steps for Testing

1. Build and deploy the notification locally
2. Start Artemis in debug mode and create a programming exercise with static code analysis enabled
3. Set break point in ResultResource.notifyNewResult
4. Alter pom.xml in the test repository to include the Checkstyle and Pmd maven plugin (example can be found https://github.com/kloessst/BambooTest/blob/master/pom.xml). Just copy those dependencies.
5. Alter the static code analysis task to match:
   
6. Alter the artifacts to match:
   
7. Participate in the programming exercise and commit bad code
8. Inspect the request body when the break point triggers
   --> Static Code Analysis reports should be part of the request body and should match the format defined in the notification plugin readme.

[sleiss]

Tested it, works fine 👍

[krusche]

Code looks good to me, I only found one issue, see my inline comment.

I wonder if we should add some automatic tests that could be executed using GitHub actions. I think this would really help in the future!