Add configurable option to limit maximum number of profile agents per account #105
Description
See: digitalbazaar/bedrock-profile-http#57
Determine the best place for implementation and configuration options on this. Perhaps also allow different maximums to be set on a given account (if a use case arises where a system-wide maximum per account is insufficient in granularity).
To start, there should be a limit based on root profile agents. Additional limits can be added later to limit the total number of profile agents, perhaps based N per profile per account, with ideally just 1 as the default. This approach would, in theory, limit the total number of profiles (and profile agents) overall.