Update RELEASE_NOTES and DBSCAN docs

RELEASE_NOTES

@@ -12,9 +12,10 @@ Current list of bugs and issues can be found at https://issues.apache.org/jira/b
 —-------------------------------------------------------------------------
 MADlib v1.19.0:
 
-Release Date: 2021-Dec-XX
+Release Date: 2022-Jan-XX
 
 NOTE: This release changes MADlib library location and updates UDF definitions.
+To ensure this change is reflected in the database, pg_ctl (for Postgres) or gpstop (for Greenplum) has to be in the PATH at the time of madpack installation.
 Views depending directly on madlib defined function(s) have to be dropped
 before upgrading.
 

src/ports/postgres/modules/dbscan/dbscan.sql_in

@@ -70,7 +70,8 @@ dbscan( source_table,
         eps,
         min_samples,
         metric,
-        algorithm
+        algorithm,
+        max_segmentation_depth
       )
 </pre>
 
@@ -162,6 +163,12 @@ a relatively small eps, so it can return the first result faster; if it looks
 like there are too many small clusters, increase eps and allow it to run for longer.
 
 </ul></dd>
+
+<dt>max_segmentation_depth (optional)</dt>
+<dd>INTEGER, default: <number of segments>. The number of regions to segment
+the data. See <b>optimized</b> for usage.
+</dd>
+
 </dl>
 
 <b>Output</b>