expose import.quiet_fallback as cli option

[mgoltzsche]

Description

Exposes the configuration option import.quiet_fallback as CLI option.

Relates to #4958.

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[Serene-Arc]

Thanks for the PR! Was thinking of implementing this one myself, so thanks personally for doing the work. Looks good and ready to merge to me.