Feature: Map flavor not found to ResourceExhausted grpc code

[viragvoros]

How to categorize this PR?
/area robustness
/kind enhancement
/platform openstack

What this PR does / why we need it:
This PR improves OpenStack machine error handling by classifying flavor resolution failures and mapping them to codes.ResourceExhausted. Previously, only NoValidHost errors were classified as resource exhausted errors.

Special notes for your reviewer:
None

Release note:

other operator
Improved OpenStack machine error handling by classifying flavor resolution failure as resource exhaustion.

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