Add User Delegation Credential and User Delgation SAS

[siminsavani-msft]

Adding the option to create a service client with UDK. Tests in progress!

• The purpose of this PR is explained in this or a referenced issue.
• The PR does not update generated files.
  • These files are managed by the codegen framework at Azure/autorest.go.
• Tests are included and/or updated for code changes.
• Updates to CHANGELOG.md are included.
• MIT license headers are included in each file.

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[jhendrixMSFT]

Fixes #18976