Support Multiple User Agent Strings in Telemetry

[ellis-wilson-ms]

In order to get Attribution for a first or third party's software or solution impact on Blob storage a Partner Attribution Tag must be provided as part of the User Agent string as part of HTTP requests associated with interaction with blockblob.

The Go SDK provides a means by which to specify a single User Agent string, sans spaces, and below 24 characters via:

https://azure.github.io/azure-sdk/general_azurecore.html#telemetry-policy

However, Partner Attribution tags frequently require more than a single User Agent string. For instance, we need all of:

"APN/1.0 MS_Azure/1.0 AMLFS/1.0"

The Azure SDK for Python supports addition of a user agents:

https://github.com/Azure/azure-sdk-for-python/blob/35d0bd03db364b102a15204ec9658be62ba929cc/sdk/core/azure-core/azure/core/pipeline/policies/_universal.py#L235

The Azure for C# SDK simply doesn’t filter for spaces or length, so you can slam three UA strings in there if you like. I realize that is at odds with the Azure SDK policy on Application IDs (<=24c and no spaces), but that policy is for a single App ID. Nothing I can see specifies that you must only have a single App ID provided.

This was discussed via email with @RickWinter, @JeffreyRichter, and @jhendrixMSFT who asked me to open this. Hopefully I have represented the problem appropriately here.

[github-actions]

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