ExternalGroupPrincipalProvider needs to cache results of local group resolution

The dynamic sync feature stores the list of external group principal names with the user account. However, if those external groups are members of local groups owned by the repository, that inherited group membership is not cached and will be re-calculated upon subsequent repository logins.

In case of a high number of inherited local groups this can lead to performance issues upon login and we should leverage the UserConfiguration configuration parameter PARAM_CACHE_EXPIRATION to also populate the information below userhome/rep:cache with the result from the group principal resolution from ExternalGroupPrincipalProvider.

this should go along with dedicated benchmarks measuring the effect.