feat: harden linux VHD builds with user-delegation SAS tokens

[cameronmeissner]

What type of PR is this?

What this PR does / why we need it:

has linux VHD builds use user-delegation SAS tokens created via the agent pool's managed identity rather than generating SAS tokens using a hard-coded connection string - this will make builds more secure by preventing risk of exposing connection string secrets, as well as capping SAS token TTL to 7 days due to user delegation key TTL constraints

Which issue(s) this PR fixes:

Fixes #

Requirements:

• [ ] uses conventional commit messages
• [ ] includes documentation
• [ ] adds unit tests
• [ ] tested upgrade from previous version

Special notes for your reviewer:

Release note:

none

[coveralls]

Pull Request Test Coverage Report for Build 8668978062

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 79.146%

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Totals
Change from base Build 8668863321:	0.0%
Covered Lines:	2372
Relevant Lines:	2997

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💛 - Coveralls

[cameronmeissner]

addressed in #4462