feat: implement access Policy public API

[roaminggypsy]

No description provided.

[wfa-reviewable]

This change is 

[SanjayVas]

Reviewed 5 of 10 files at r1, 5 of 5 files at r2, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @roaminggypsy)

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src/main/kotlin/org/wfanet/measurement/access/service/Errors.kt line 326 at r2 (raw file):

  ServiceException(
    Errors.Reason.POLICY_ALREADY_EXISTS,
    "Policy $name already exists",

This shouldn't take the name as you can get an ALREADY_EXISTS for other reasons, such as a policy (with possibly a different name) already existing for the specified protected resource. The backend doesn't have a great way to distinguish which case it is, so we can't either.

[roaminggypsy]

Reviewable status: 7 of 10 files reviewed, 1 unresolved discussion (waiting on @SanjayVas)

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src/main/kotlin/org/wfanet/measurement/access/service/Errors.kt line 326 at r2 (raw file):

Previously, SanjayVas (Sanjay Vasandani) wrote…

This shouldn't take the name as you can get an ALREADY_EXISTS for other reasons, such as a policy (with possibly a different name) already existing for the specified protected resource. The backend doesn't have a great way to distinguish which case it is, so we can't either.

Ohhh okay. I was thinking about the inconsistency in RoleAlreadyExists and PrincipalAlreadyExists. The principal one does not take name as a param, but the role one does.

[SanjayVas]

Reviewed 3 of 3 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @roaminggypsy)

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src/main/kotlin/org/wfanet/measurement/access/service/Errors.kt line 326 at r2 (raw file):

Previously, roaminggypsy (Lin) wrote…

Ohhh okay. I was thinking about the inconsistency in RoleAlreadyExists and PrincipalAlreadyExists. The principal one does not take name as a param, but the role one does.

The Role one actually has the same problem, I just didn't catch it in previous code review. The only ALREADY_EXISTS error where we know the cause for sure is POLICY_BINDING_MEMBERSHIP_ALREADY_EXISTS.

[roaminggypsy]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @roaminggypsy)

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src/main/kotlin/org/wfanet/measurement/access/service/Errors.kt line 326 at r2 (raw file):

Previously, SanjayVas (Sanjay Vasandani) wrote…

The Role one actually has the same problem, I just didn't catch it in previous code review. The only ALREADY_EXISTS error where we know the cause for sure is POLICY_BINDING_MEMBERSHIP_ALREADY_EXISTS.

Got it I will fix that in another PR.