text: Title: Document that failing test setup stops execution even if continue-on-failure mode is active
  Body: When support for controlling the continue-on-failure mode was added (#2285), we didn't think how tests setups should behave when the mode is activated. Currently if you have a test like
  ```robotframework
  *** Test Cases ***
  Example
      [Tags]    robot:continue-on-failure
      [Setup]     Setup Keyword
      Keyword In Body
      Another Keyword
  ```
  and the `Setup Keyword` fails, keywords in the test body aren't run. That can be considered inconsistent because continue-on-failure mode is explicitly enabled, but I actually like this behavior. You can have some action in setup so that execution ends if it fails, but keywords in the body that are validating that everything went as expected would all be run if the setup succeeds. This would also add some new functionality to setups that are otherwise not really different from normal keywords.
  
  What do others (especially @oboehmer) think about this? Should we stop execution after a failing setup also when continue-on-failure mode is on? If yes, we just need to add some tests for the current behavior and mention this in the User Guide. If not, then we need to change the code as well.
  
  A problem with changing the code is that the change would be backwards incompatible. It's a bit questionable could we do it without a deprecation in RF 5.1 but deprecation adds more work.
  