[New Feature]: Support *_limit field configurations for titiler-pgstac

[tariqksoliman]

• scan_limit
  integer | (integer | null)(query) | Return as soon as we scan N items (defaults to 10000 in PgSTAC).

• items_limit
  integer | (integer | null)(query) | Return as soon as we have N items per geometry (defaults to 100 in PgSTAC).

• time_limit
  integer | (integer | null)(query) | Return after N seconds to avoid long requests (defaults to 5 in PgSTAC).