Orgs with paid quota can use 10mb rds instance [fixes #49420959]

Includes a significant refactor of Models::ServiceInstance#check_quota
and Models::Organization#service_plan_quota_remaining? methods.
Remove hard-coding of trial_db identifier [finishes #49420959]

trial_db_guid is now configurable in the cc yaml with this stanza:

trial_db:
  guid: <trial db service_plan guid>
Seed db with separate system and app domains

[#49220887]
Allow setting system domain as an app domain
Update vcap_common and accept optional dashboard_url passed from the gateway.
refactor to pull out some seed data stuff from the model classes
add the actual seeds
update schema to allow NilClass for system_domain_orginazation
stager: add upload and download to the droplet and buildpack_cache uris so that nginx doesn't swallow download requests from deas
fixed quota definition flaky test
Fix .ruby-version
Merge remote-tracking branch 'github/master' into
OracleSupportSingleCommit

Conflicts:
	lib/cloud_controller/models/quota_definition.rb
	spec/models/quota_definition_spec.rb