More detailed error reporting on import fails

Is your feature request related to a problem? Please describe.

There are plenty of broken ics files out there. We already try our best to fix them with the repair-steps.
Nonetheless, we can't fix everything.

Describe the solution you'd like
Parse the response message when import fails and check for a Sabre error code:

• UnsupportedMediaType or ParseException for syntax errors
• NoInstancesException for error like this one
• Are there more relevant?

We can use the responses for more detailed error messages in the console.
If we end up with a NoInstancesException, we might just count it as a successful import, because it contains no events to import anyway.

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Start by reading the import and parser code around src/parsers/repairsteps/icalendar, then trace how failed import responses reach the console. Identify the Sabre error codes that are available and define the expected handling for syntax errors and imports with no instances. Done means import failures provide more specific console messages and the no-instances case is handled consistently.