Add configurable limits for number of builds allowed under a namespace

We also support that limit being increased automatically once a successful billing charge has gone through

util/config/schema.py

@@ -45,7 +45,6 @@ INTERNAL_ONLY_PROPERTIES = {
   'SYSTEM_SERVICE_BLACKLIST',
   'JWTPROXY_SIGNER',
   'SECURITY_SCANNER_INDEXING_MIN_ID',
-  'MAX_BUILD_QUEUE_RATE_SECS',
   'STATIC_SITE_BUCKET',
   'LABEL_KEY_RESERVED_PREFIXES',
   'TEAM_SYNC_WORKER_FREQUENCY',
@@ -65,13 +64,14 @@ INTERNAL_ONLY_PROPERTIES = {
   'MAIL_FAIL_SILENTLY',
   'LOCAL_OAUTH_HANDLER',
   'USE_CDN',
-  'MAX_BUILD_QUEUE_RATE_ITEMS',
   'ANALYTICS_TYPE',
 
   'EXCEPTION_LOG_TYPE',
   'SENTRY_DSN',
   'SENTRY_PUBLIC_DSN',
 
+  'BILLED_NAMESPACE_MAXIMUM_BUILD_COUNT',
+
   'SECURITY_SCANNER_ENDPOINT_BATCH',
   'SECURITY_SCANNER_API_TIMEOUT_SECONDS',
   'SECURITY_SCANNER_API_TIMEOUT_POST_SECONDS',
@@ -699,6 +699,11 @@ CONFIG_SCHEMA = {
       'description': 'Whether to support Dockerfile build. Defaults to True',
       'x-example': True,
     },
+    'DEFAULT_NAMESPACE_MAXIMUM_BUILD_COUNT': {
+      'type': ['number', 'null'],
+      'description': 'If not None, the default maximum number of builds that can be queued in a namespace.',
+      'x-example': 20,
+    },
 
     # Login
     'FEATURE_GITHUB_LOGIN': {