PRICE-2642 - Add 503 service unavailable details in DELETE price list and price records endpoints

[bc-vinbase]

PRICE-2642

What changed?

Adds 503 error response documentation to the following DELETE endpoints in price_lists.v3.yml:

• DELETE /pricelists — Delete All Price Lists
• DELETE /pricelists/{price_list_id} — Delete a Price List
• DELETE /pricelists/{price_list_id}/records — Delete Price List Records
• DELETE /pricelists/{price_list_id}/records/{variant_id}/{currency_code} — Delete a Price Record by
  Currency Code

Also adds a new ServiceUnavailableError schema to components/schemas with the following fields: code,
message, details, retry_after_seconds, and timestamp.

These endpoints now return 503 when the service is temporarily degraded, with a SERVICE_DEGRADED error
code and a retry_after_seconds field indicating when the client should retry.

Release notes draft

The DELETE endpoints for Price Lists and Price List Records now return a 503 response when the
service is temporarily unavailable. If you receive this response, check the retry_after_seconds field
in the response body to know when to retry your request.

ping @bc-rogersepulveda @VivekV95 @bdav87