New major version to remove legacy features

[strangelookingnerd]

This PR is starting a new major version and removes deprecations introduced in 2.0. See #151

It has been a year since 2.0 was released, giving users and consumers of the plugin time to migrate away from any legacy configuration / API.

The main reason to remove the legacy features for me is that the maintenance is harder than it needs to be and technical dept should be reduced.

If @jenkinsci/badge-plugin-developers have any objections regarding this change, please let me know. I will leave the PR open for a while to gather feedback.

Testing done

mvn clean verify

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[MarkEWaite]

I would like more time to review the impact of the changes. If the changes are large enough that they require users to modify their Pipeline definitions, there will be a major outcry from users. However, I won't have time this week to evaluate the changes.