Add a possibility to add custom roles definitions for julieops

[purbon]

• Please check if the PR fulfills these requirements

• The commit messages are descriptive
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• An issue has been created for the pull requests. Some issues might require previous discussion.

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

This PR is an upcoming feature request that will allow users to add their own custom role definitions. So no more only consumer, producer, connectors, streams and ksqls, but now you can extend your own if desired.

• What is the current behavior? (You can also link to an open issue here)

Currently, there is no option to add any custom role definition, users has to stick to the current ones.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

No, as it only adds new functionality. In the future even the old roles could be moved from code definition into the configuration, simplifying most probably the necessary code in the application.

• Other information:

IMPORTANT: Please review the CONTRIBUTING.md file for detailed contributing guidelines.
IMPORTANT: Your pull request MUST target master.

closes #300