Problem/Motivation
In #2921810: Allow TimestampFormatter to show as a fully cacheable time difference with JS, a time diff formatting option is provided. Part of that implementation was a "fallback configuration", labeled 'description'. No config schema was added for description, leading to situations where my CI build fails that validates configuration.
Steps to reproduce
Have schema validator enabled; add a timestamp field to a view; try saving the view. Expected: the view gets saved. Actual: a config schema validation exception is thrown.
Proposed resolution
Provide the missing schema (the MR does this).
Remaining tasks
Fix the tests.
User interface changes
None.
API changes
None.
Data model changes
None.