Add a new option for filtering to a subset of directory groups in the
Pomerium JWT and Impersonate-Group headers. Add a JWTGroupsFilter field
to both the Options struct (for a global filter) and to the Policy
struct (for per-route filter). These will be populated only from the
config protos, and not from a config file.
If either filter is set, then for each of a user's groups, the group
name or group ID will be added to the JWT groups claim only if it is an
exact string match with one of the elements of either filter.
* Optimize policy iterators (go1.23)
This modifies (*Options).GetAllPolicies() to use a go 1.23 iterator
instead of copying all policies on every call, which can be extremely
expensive. All existing usages of this function were updated as
necessary.
Additionally, a new (*Options).NumPolicies() method was added which
quickly computes the number of policies that would be given by
GetAllPolicies(), since there were several usages where only the
number of policies was needed.
* Fix race condition when assigning default envoy opts to a policy
