Add query facility for client management servlet

[jjg-123]

A scenario that has popped up a few times is that an admin wants to register clients, but has no way to determine if their requests for various lifetimes make sense. The well -known page does not have these. I propose allowing a query to GET that will return server defaults, so

https://.../oidc-cm?query=org.oa4mp:/server/defaults

returns something like

{
  at_lifetime:1009,
  id_token_lifetime:900,
  rt_lifetime:1296000,
  max_at_lifetime:19600,
  max_rt_lifetime:2592000,
  auth_grant_lifetime:750,
  max_id_token_lifetime:1800,
  rtGracePeriod:3600
 }

(all in seconds) allowing admins to make sane requests.

[jjg-123]

See https://oa4mp.org/server/manuals/dynamic-client-registration.html#get_defaults which is the section "getting server defaults"