Fail when specified configuration profile doesn't exist

Since MAGNOLIA-7781 a configuration profile can be specified through the MAGNOLIA_PROFILE environment variable. If such a profile does not exist Magnolia silently falls back to the default profile. We should change this and make Magnolia fail in such a case. (If explicitly specified the default profile could still be used).

To implement this we need to clarify what it means for a profile to exist. As an initial approach I suggest to only implement this for the case where PROFILE_INITIALIZATION_PARAMETER is not overridden and in this case fail if the directory WEB-INF/config/${env/MAGNOLIA_PROFILE} does not exit. Further refinements like checking if the directory is non empty or even whether it contains files that are actually resolved would be possible but could easily become unwieldy.