[keyserver] Strip member.permissions for FUTURE_CODE_VERSION clients

Summary:
Add stripMemberPermissions option to rawThreadInfoFromServerThreadInfo to strip member permissions for new clients.

Depends on D12763

Test Plan:
Did some basic testing where I hardcoded stripMemberPermissions being passed to rawThreadInfoFromServerThreadInfo and set breakpoints to check output.

Will do additional testing with validators + after getting basic client migration working.

With stripMemberPermissions=false:

(can observe that each of the two members have permissions field set to string)

With stripMemberPermissions=true:

Reviewers: ashoat, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D12779