Minor version bump v0.2.0

[munterfi]

@clukas1, I have seen the release tag you made yesterday. Unfortunately the version in the pom.xlm was not adjusted accordingly, which will lead to conflicts wth the maven artifact and docker image to be published.

Therefore i deleted the tag.

I would propose the following steps to release versions:

• Checkout a new branch release/vX.X.X
• Set version number in pom.xml and prepare other documentation if needed
• Create pull request, optionally with a release description, to be copied into the release later.
• Upon merge of pull request, create a new release using the GitHub web interface and name it public-transit-service X.X.X, which then triggers the correct GitHub action for maven release and docker publish.

What do you think? @clukas1 @Brunner246

[munterfi]

If you are OK with this procedure, I would add it to the project documentation page.