319 - test and push helm charts to github pages

[Knappek]

Description

• lints and tests helm charts on pull requests
• releases helm charts on github pages when merging to master

Closes #319

What to look out for

Dear reviewer, I want you to

• gain knowledge - I think it's important for you to know about the change.
• check that the code works on your machine.
• suggest implementation-code design/structure/readability improvements.
• suggest test-code design/structure/readability improvements.
• suggest documentation improvements.
• suggest language/writing improvements.
• help to find bugs (described below!).

Process

The goal is to improve not only the code in this PR but also our skills! The "rules":

• The review is considered "done" as soon as all reviewers have added their review, and all their comments have been addressed.
• For knowledge-sharing reviews, each reviewer should "approve" the PR after studying its content.
• After the approval, the merge is concluded by the developer.

Have fun!