local-rate-limit: add descriptor fill_interval lower bound

[adisuissa]

Commit Message: local-rate-limit: add descriptor fill_interval lower bound
Additional Description:
The local-rate-limit filter has a lower-bound fill_interval validation for the non-descriptor field.
This PR adds the same lower-bound to the fill_interval of a descriptor.
Note that this will reject previously valid configs that were under 50msec. In this case the config must change to be at least 50msec.

This was found by a fuzz test.

Risk Level: low
Testing: Added fuzz test corpus
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

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Caused by: #37375 was opened by adisuissa.

see: more, trace.