Enable configurable 'maxBatchChanges' limit

One use case is when a group is responsible for importing
large batches of changes delivered from external partners,
and those changes all require review. This group, and only
this group, should be allowed to bypass the limit that is
enforced for everyone else.

Allow site administrators to configure the 'maxBatchChanges'
limit for users from global capability UI of All-Projects
access. The min box does not make sense if its value is not 0,
so disable it after giving it the default value of 0.

The effective limit value will be the capability value if it
exists, or the value in gerrit.config if it exists, or else
no limit.

Change-Id: Ic929dc4a89cc8ccbd098035ce2ceac4f22fd54da

Documentation/access-control.txt

diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index e814daf..e500e4a 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -1158,6 +1158,20 @@
 capabilities granted to them automatically.
 
 
+[[capability_batchChangesLimit]]
+=== Batch Changes Limit
+
+Allow site administrators to configure the batch changes limit for
+users to override the system config
+link:config-gerrit.html#receive.maxBatchChanges['receive.maxBatchChanges'].
+
+Administrators can add a global block to `All-Projects` with group(s)
+that should have different limits.
+
+When applying a batch changes limit to a user the largest value
+granted by any of their groups is used. 0 means no limit.
+
+
 [[capability_createAccount]]
 === Create Account