Custom scopes support in M2M and WIF

[Tejas-Kochar]

Summary

• Refactor M2M and WIF to use get_scopes

How is this tested?

• Integration tests with mocking for M2M and WIF to ensure correct scopes propogated correctly to token requests.

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NO_CHANGELOG=true

[github-actions]

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Trigger:
go/deco-tests-run/sdk-py

Inputs:

• PR number: 1167
• Commit SHA: 916ab888cf6bd8dbd58ce3e888b529e947488cfd

Checks will be approved automatically on success.