prepare release 9.1.0

[tomuben]

All Submissions:

• Check if your pull request goes to the correct bash branch (develop or master)?
• Is the title of the Pull Request correct?
• Is the title of the corresponding issue correct?
• Have you updated the changelog?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Are you mentioning the issue which this PullRequest fixes ("Fixes...")

When integrating to Develop branch:

1. Remember to merge with "Squash and Merge"

When integrating to Main branch:

1. Remember to merge with "Merge"
2. Have you thought about version number? If there is a breaking change in the toolchain, need to update major version.
3. If you plan a release, have you checked the Exasol packages for updates?
   1. Websocket API (https://github.com/EXASOL/websocket-api)
   2. Exasol-BucketFS