Update TextAnalytics to enable live testing in sovereign clouds for multiple services

[v-xuto]

These changes enable textanalytics to run live tests against Public, UsGov and China.

1. As suggested in the issue [Text Analytics]"Unauthorized. Access token is missing, invalid, audience is incorrect (https://cognitiveservices.azure.us), or have expired." in USGOV and China #21448,
   So update text_analytics = TextAnalyticsClient(textanalytics_test_endpoint, token) in test_auth.py(async)
   to:

   text_analytics_endpoint_suffix = os.environ.get("TEXTANALYTICS_ENDPOINT_SUFFIX",".cognitiveservices.azure.com")
   credential_scopes = ["https://{}/.default".format(text_analytics_endpoint_suffix[1:])]
   text_analytics = TextAnalyticsClient(textanalytics_test_endpoint, token, credential_scopes=credential_scopes)
   

2. As suggested in the issue [Text Analytics] "Invalid URL '$(js-textanalytics-test-service-endpoint)/text/analytics/v3.2-preview.2/analyze': No schema supplied" in Public, USGOV and China clouds #22281,
   move MatrixReplace: - TestSamples=.*/true to the PublicCloud config in test.yaml, and skip these tests related to env textanalytics_custom_text_endpoint in usgov and china clouds.

Besides, in order to solve the error:KeyError: 'TEXTANALYTICS_CUSTOM_TEXT_ENDPOINT' in most tests,
add code TextAnalyticsCustomPreparer in files test_analyze.py(async) and update TextAnalyticsPreparer in testcase.py.

Pipeline results:
https://dev.azure.com/azure-sdk/internal/_build/results?buildId=1289623&view=results

@benbp, @kristapratico, @jameszliao-msft, @lmazuel, @meeraharidasa , @mayurid, @abhahn for notification.

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[iscai-msft]

why are these variables moved from the testcase to the test files?

[kristapratico]

If I'm not mistaken, they needed to be separated since these env vars don't exist in the UsGov/China cloud.

[v-xuto]

@kristapratico @iscai-msft If I don't remove these variables, I'll get an error when rerun textanalytics weekly pipeline. Error message: azure_devtools.scenario_tests.preparers:preparers.py:82 Preparer failure when creating resource PowerShellPreparer for test <test_auth.TestAuth object at 0x111e26190>: 'TEXTANALYTICS_CUSTOM_TEXT_ENDPOINT'
For more details please check here.

For example test_auth.py::TestAuth::test_active_directory_auth, I have debugged this test locally. When the code is executed to devtools_testutils/powershell_preparer.py , it will get the corresponding values of these variables ( in TextAnalyticsPreparer) from the environment variables one by one, if not, an exception will be thrown. Because the values of these variables are not passed in UsGov/China cloud, the test will fail before the testcase actually runs.

So I moved variables from the testcase to the test files. Or do you have better suggestions?

[kristapratico]

Thanks for all your work on this @v-xuto!

[v-xuto]

@benbp Please review this PR when you are free. Thanks.

[benbp]

Thank you @v-xuto!