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

config.py

@@ -451,12 +451,6 @@ class DefaultConfig(ImmutableConfig):
   # Location of the static marketing site.
   STATIC_SITE_BUCKET = None
 
-  # Count and duration used to produce a rate of builds allowed to be queued per repository before
-  # rejecting requests. Values less than zero disable rate limiting.
-  # Example: 10 builds per minute is accomplished by setting ITEMS = 10, SECS = 60
-  MAX_BUILD_QUEUE_RATE_ITEMS = -1
-  MAX_BUILD_QUEUE_RATE_SECS = -1
-
   # Site key and secret key for using recaptcha.
   FEATURE_RECAPTCHA = False
   RECAPTCHA_SITE_KEY = None
@@ -507,3 +501,10 @@ class DefaultConfig(ImmutableConfig):
   # If enabled, ensures that API calls are made with the X-Requested-With header
   # when called from a browser.
   BROWSER_API_CALLS_XHR_ONLY = True
+
+  # If set to a non-None integer value, the default number of maximum builds for a namespace.
+  DEFAULT_NAMESPACE_MAXIMUM_BUILD_COUNT = None
+
+  # For Billing Support Only: The number of allowed builds on a namespace that has been billed
+  # successfully.
+  BILLED_NAMESPACE_MAXIMUM_BUILD_COUNT = None