[text analytics] add perf tests

sdk/textanalytics/azure-ai-textanalytics/tests/perfstress_tests/README.md

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+# Text Analytics Performance Tests
+
+In order to run the performance tests, the `azure-devtools` package must be installed. This is done as part of the `dev_requirements` install.
+Start by creating a new virtual environment for your perf tests. This will need to be a Python 3 environment, preferably >=3.7.
+
+### Setup for test resources
+
+The following environment variable will need to be set for the tests to access the live resources:
+
+```
+AZURE_TEXT_ANALYTICS_ENDPOINT=<text analytics service endpoint>
+AZURE_TEXT_ANALYTICS_KEY=<text analytics API Key>
+```
+
+### Setup for perf test runs
+
+```cmd
+(env) ~/azure-ai-textanalytics> pip install -r dev_requirements.txt
+(env) ~/azure-ai-textanalytics> pip install -e .
+```
+
+## Test commands
+
+When `azure-devtools` is installed, you will have access to the `perfstress` command line tool, which will scan the current module for runable perf tests. Only a specific test can be run at a time (i.e. there is no "run all" feature).
+
+```cmd
+(env) ~/azure-ai-textanalytics> cd tests/perfstress_tests/
+(env) ~/azure-ai-textanalytics/tests/perfstress_tests> perfstress
+```
+Using the `perfstress` command alone will list the available perf tests found.
+
+### Common perf command line options
+These options are available for all perf tests:
+- `--duration=10` Number of seconds to run as many operations (the "run" function) as possible. Default is 10.
+- `--iterations=1` Number of test iterations to run. Default is 1.
+- `--parallel=1` Number of tests to run in parallel. Default is 1.
+- `--warm-up=5` Number of seconds to spend warming up the connection before measuring begins. Default is 5.
+- `--sync` Whether to run the tests in sync or async. Default is False (async). This flag must be used for Storage legacy tests, which do not support async.
+- `--no-cleanup` Whether to keep newly created resources after test run. Default is False (resources will be deleted).
+
+## Example command
+```cmd
+(env) ~/azure-ai-textanalytics/tests/perfstress_tests> perfstress DetectLanguagePerfStressTest
+```

sdk/textanalytics/azure-ai-textanalytics/tests/perfstress_tests/perf_detect_language.py

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+# coding=utf-8
+# ------------------------------------
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+# ------------------------------------
+import os
+from azure_devtools.perfstress_tests import PerfStressTest
+from azure.core.credentials import AzureKeyCredential
+from azure.ai.textanalytics import TextAnalyticsClient
+from azure.ai.textanalytics.aio import TextAnalyticsClient as AsyncTextAnalyticsClient
+
+class DetectLanguagePerfStressTest(PerfStressTest):
+    def __init__(self, arguments):
+        super().__init__(arguments)
+
+        # test related env vars
+        endpoint = os.environ["AZURE_TEXT_ANALYTICS_ENDPOINT"]
+        key = os.environ["AZURE_TEXT_ANALYTICS_KEY"]
+
+        # assign the clients that will be used in the perf tests
+        self.service_client = TextAnalyticsClient(
+            endpoint=endpoint,
+            credential=AzureKeyCredential(key),
+        )
+        self.async_service_client = AsyncTextAnalyticsClient(
+            endpoint=endpoint,
+            credential=AzureKeyCredential(key),
+        )
+
+    async def close(self):
+        """This is run after cleanup."""
+        await self.async_service_client.close()
+        self.service_client.close()
+        await super().close()
+
+    def run_sync(self):
+        """The synchronous perf test."""
+        self.service_client.detect_language(["This is in English"])
+
+    async def run_async(self):
+        """The asynchronous perf test."""
+        await self.async_service_client.detect_language(["This is in English"])