Manually created branches should be cleaned up by default

When I manually create a branch build for a plan, the Do not clean up this plan branch automatically flag is set by default. While this is nice for long running branches not changing very often, it is a PITA for a heavy traffic plan where devs quickly create a branch build on their own for various reasons. Even if their issue branches would match the automatic branch expression, they are not cleaned up and all the artifacts stay on the server forever until a human bot runs through the list of branches and cleans them up manually.

Instead I suggest to change the default of the flag the other way around: it is unchecked by default. So branches matching the branch expression are cleaned up properly after X days regardless whether they are created manually or picked up by the change detection. Using a branch name not matching the expression still would prevent the cleanup, even with the flag unchecked.