GH move from master to main branch

[simonkowallik]

The since some time the main branch is the new default branch while the master branch still exists and holds, now outdated, data.

This can cause issues for those who bookmarked content within the master branch or regularly try retrieve the newest data from master.

Maybe it should be considered clearing the master branch with a clear notification that main in the new default branch.

Permalinks for master would continue to work as they target specific commits, so there should not be any harm.

[JuergenMang]

Such issues could be prevented: https://github.com/F5Networks/f5-appsvcs-extension/issues/861