[azeventhubs/azservicebus] Adding some readmes for the stress tests in case anyone else wants to try it out. (Azure#20829)

Gives a light introduction to what the structure is, and a link to the documentation.

Fixes Azure#19256

Author: richardpark-msft

sdk/messaging/azeventhubs/internal/eh/stress/readme.md

@@ -0,0 +1,28 @@
+# Event Hubs package reliability tests
+
+These are the stress/reliability tests for the `azeventhubs` package.
+
+The entrypoint for the tests is [`stress.go`](https://github.com/Azure/azure-sdk-for-go/blob/main/sdk/messaging/azeventhubs/internal/eh/stress/stress.go). All of the individual tests are in the `tests` sub-folder. These tests should run fine on your local machine - you'll need to create an `.env` file, in the root of the `azeventhubs` module, with the following values:
+
+```bash
+EVENTHUB_CONNECTION_STRING=<connection string to the Event Hubs namespace>
+EVENTHUB_NAME=<already created Event Hub - should have at least 4 partitions>
+CHECKPOINTSTORE_STORAGE_CONNECTION_STRING=<connection string to an Azure Storage account>
+APPINSIGHTS_INSTRUMENTATIONKEY=<instrumentation key for appinsights>
+```
+
+There are two types of tests - batch and processor. Each test takes a variety of flags to control the duration, number of events, etc..
+
+For instance, to run a `Processor` test to receive events:
+
+```bash
+go run . processor
+```
+
+To see more options just run:
+
+```bash
+go run . processor --help
+```
+
+For convenience there's a deploy.ps1 file that'll launch the deployment - by default it'll go to the `pg` cluster, which we use for adhoc workloads. For more information about prerequisites look at the official stress test docs here: [stress test readme.md](https://github.com/Azure/azure-sdk-tools/tree/main/tools/stress-cluster/chaos).

sdk/messaging/azservicebus/internal/stress/readme.md

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+# Service Bus package reliability tests
+
+These are the stress/reliability tests for the `azservicebus` package.
+
+The entrypoint for the tests is [`stress.go`](https://github.com/Azure/azure-sdk-for-go/blob/main/sdk/messaging/azservicebus/internal/stress/stress.go). All of the individual tests are in the `tests` sub-folder. These tests should run fine on your local machine - you'll need to create an `.env` file with the following values:
+
+```bash
+SERVICEBUS_CONNECTION_STRING=<connection string to the Service Bus namespace>
+APPINSIGHTS_INSTRUMENTATIONKEY=<instrumentation key for appinsights>
+```
+
+To run one of the more basic tests, where we just send and receive messages for a few days:
+
+```bash
+go run . tests infiniteSendAndReceive
+```
+
+To see all the tests that are available:
+
+```bash
+go run . tests
+```
+
+For convenience there's a deploy.ps1 file that'll launch the deployment - by default it'll go to the `pg` cluster, which we use for adhoc workloads. For more information about prerequisites look at the official stress test docs here: [stress test readme.md](https://github.com/Azure/azure-sdk-tools/tree/main/tools/stress-cluster/chaos).