[CLU+QA] update polling_interval per service recommendation

[kristapratico]

Resolves #26108 #26109

Request from the service team to update the default polling_interval to 5 seconds for both QA and CLU. This was previously defaulting to the azure-core default of 30 seconds.

[kristapratico]

/azp run python - cognitivelanguage - tests

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[azure-sdk]

API change check

API changes are not detected in this pull request.

[heaths]

.NET defaults to 1s unless the Retry-After header is sent. @peytonfraser @kayousef why isn't the service sending this header if that's what it recommends?

[kristapratico]

.NET defaults to 1s unless the Retry-After header is sent. @peytonfraser @kayousef why isn't the service sending this header if that's what it recommends?

Just to give background, in Text Analytics we've always used 5 secs from what the service team recommended a long time ago. This is updating CLU and QA to use the same per my conversation with Mikael.

The 5 seconds is used as the initial polling interval between the POST and the first GET (before we have a chance to see a Retry-After header). After that, if the service returns a Retry-After header, then that's what is used in subsequent calls (like .NET).