[stress testing] Update docs, resiliency for deploy script

[benbp]

Updates the stress test docs to use commands from the stress test deploy script instead of the multi-step manual commands.

Updates the stress test script to handle different az subscription contexts in all scenarios, and a bug fix for auto-installing the powershell yaml module.

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[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[ghost]

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[benbp]

/check-enforcer override