Enhance import logging

Is your feature request related to a problem? Please describe.
The logging routines during import are rather basic. Mostly, the user just gets a message that the server could not import a recipe from a remote site. For debugging and user experience, it would be very nice to have a cleaner output.

It might be even thinkable to have a debug output that simplifies debugging the solution on the machine. E.g. an export of the downloaded HTML data and the extracted intermediate steps might be a feasible solution. These could be prepared internally on a temp folder and cleaned after a certain time frame (1 day or so).

Describe the solution you'd like
Clear logging is essential for users.
Debugging might help sort out issues of the import scripts.

Describe alternatives you've considered
Give only access to the information of failure to the admin via logging to the nextcloud.log file. This would reduce the security related considerations a bit.

No files, tests, or entry points are named. Start by locating the import logging routines and reviewing how failures are written to nextcloud.log; clarify the desired scope for clearer messages, optional downloaded-HTML and intermediate-step debug output, temporary storage, and cleanup before implementation.