Doc: Add diskquota license for ASF compliance

Add diskquota extension license information to comply with Apache
release requirements.

Changes:
- Add diskquota entry to top-level LICENSE file under Greenplum section
- Create licenses/LICENSE-diskquota.txt with PostgreSQL License text
- Add gpcontrib/diskquota/** to pom.xml excludes for apache-rat checks

The diskquota extension is licensed under the PostgreSQL License,
originally developed by Pivotal Software and VMware.

Author: tuhaihe

LICENSE

@@ -311,12 +311,18 @@ The Greenplum Database software includes:
       gpcontrib/orafce/*
       see licenses/LICENSE-orafce.txt
 
- ----------------------------
+----------------------------
    BSD 3 Clause License
 
       gpcontrib/gpcloud/test/googletest
       see licenses/LICENSE-googletest.txt
 
+----------------------------
+   PostgreSQL License
+
+      gpcontrib/diskquota/*
+      see licenses/LICENSE-diskquota.txt
+
 ================================================================================
 Apache Cloudberry includes codes from
 

licenses/LICENSE-diskquota.txt

@@ -0,0 +1,31 @@
+Copyright (c) 2004-2020 Pivotal Software, Inc.
+Copyright (c) 2020-Present VMware, Inc. or its affiliates
+
+diskquota is licensed under the PostgreSQL license, the same license
+as PostgreSQL. It contains parts of PostgreSQL source code. A copy of
+the license is below:
+
+--------------
+PostgreSQL Database Management System
+(formerly known as Postgres, then as Postgres95)
+
+Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+
+Portions Copyright (c) 1994, The Regents of the University of California
+
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose, without fee, and without a written agreement
+is hereby granted, provided that the above copyright notice and this
+paragraph and the following two paragraphs appear in all copies.
+
+IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
+DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+
+THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO
+PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.

pom.xml

@@ -153,6 +153,8 @@ code or new licensing patterns.
             <exclude>gpcontrib/gp_exttable_fdw/data/**</exclude>
             <exclude>gpcontrib/gp_exttable_fdw/gp_exttable_fdw.control</exclude>
 
+            <exclude>gpcontrib/diskquota/**</exclude>
+
             <exclude>getversion</exclude>
             <exclude>.git-blame-ignore-revs</exclude>
             <exclude>.dir-locals.el</exclude>