Download and compare linux-musl-x64 MSFT sdk

[ellahathaway]

Addresses dotnet/source-build#3714

This PR:

• Fixes the regex used for downloading the MSFT sdk so that it now matches linux-musl-x64 as done in 6.0
• Adds in a portable rid for linux-musl. This now matches the portableRid for linux-musl in 6.0

Azdo pipeline run with these changes: https://dev.azure.com/dnceng/internal/_build/results?buildId=2317704&view=results

[mthalman]

It doesn't look like this is doing what it's supposed to yet. Looking at the output in the .trx file for the Alpine leg, I see this: Executing: tar tf /BlobArtifacts/dotnet-sdk-7.0.115-linux-x64.tar.gz. That would indicate the test is still referencing the linux-x64 tarball instead of the linux-musl-x64 tarball.

[ellahathaway]

Looking at the output in the .trx file for the Alpine leg, I see this: Executing: tar tf /BlobArtifacts/dotnet-sdk-7.0.115-linux-x64.tar.gz

I completely missed this. Thank you for pointing it out! These changes should be addressed in 1538ad0.

The current issue I'm facing is that the pipeline is setting the PortableRid to linux-x64 instead of linux-musl-x64. As a result, this pipeline run fails the SDK content test because the RID is not being parsed out correctly. I will update this PR once I have determined the cause of this.

Edit: Confirmed that the changes work (had to do a run of the official installer ci on my branch and consume that run in the tarball pipeline): https://dev.azure.com/dnceng/internal/_build/results?buildId=2319692&view=logs&j=da6acb1f-3c5f-5ef6-22ae-5fcf343f6bd9&t=91f6af53-1a55-52eb-e2a8-794ecfaa0886