Dev/anasanc/pep addingcommonextensioncode

[alsanmsft]

Changes here implement functions that will be frequently used across different extensions for a feature called Constrained Extensions. Constrained extensions limits the capabilities of onboarded extensions according to a customer-defined, pre-set policy.

The changes in this PR include:

• LoadPolicySettings() to load policy settings into a struct (defined by an extension) from the policy file
• ValidateFileHashInAllowlist() to implement allowlist logic into extensions that run scripts.
• ComputeFileHash()
• ValidateItemInList()
• UTs

[jscalev]

What I'm wondering is whether the search should be done case insensitive. That seems to make sense to me.

Also not a bad idea to trim the values.

[jscalev]

Looks good overall. Had one small comment.

If you haven't done so already, I recommend asking AI if more unit tests are recommended (and to write them).