Group Policy for controlling sources

[florelis]

Adding enforcement of Group Policies for additional required sources and allowed sources. This change includes:

• Reading of source lists from Group Policy. Each source is specified by a JSON with all its details.
• A new GroupPolicyException type for reporting errors.
• Enforcement of the policies when adding and removing sources (only allow adding allowed sources and don't allow removing additional required sources).
• A source export command to produce the JSON strings used in the policies.
• Unit tests.

Still pending for Group Policies:

• E2E tests
• Use final registry key path, value names, and policy names

Microsoft Reviewers: Open in CodeFlow

[JohnMcPMS]

Not that it matters much for the general use case, but I would err toward making the caller keep the value while they wanted it rather than the iterator getting the value while iterating. If I wanted to skip ahead for some reason this way reads every value anyway.

[JohnMcPMS]

Approving with the assumption that changes to resolve the test failures will be minor.

[florelis]

Two tests failed. One was because in one test for failure adding a disabled default source I needed to add the Type in the test to fit the Arg+Type matching (where I only used the Arg before). The other was because I had a test for the Data+Identifier check after adding the source; I removed the test since that check was removed.