Add new event Segment.filterSegments (#18713)

* Add new event Segment.filterSegments

For many other `*.add*` events we also have matching `.filter*` events. However, it doesn't seem to be the case for segments. 

Eg we have this for `Access.Capability.filterCapabilities`, `Dimension.filterDimensions`, `Metric.filterMetrics`, `Report.filterReports`.

* Update CHANGELOG.md

1 files changed, 14 insertions, 0 deletions

diff --git a/core/Segment/SegmentsList.php b/core/Segment/SegmentsList.php
index 82ea86065e..448a4f1593 100644
--- a/core/Segment/SegmentsList.php
+++ b/core/Segment/SegmentsList.php
@@ -132,6 +132,20 @@ class SegmentsList
             $dimension->configureSegments($list, new DimensionSegmentFactory($dimension));
         }
 
+        /**
+         * Triggered to filter segment definitions.
+         *
+         * **Example**
+         *
+         *     public function filterSegments(&$segmentList)
+         *     {
+         *         $segmentList->remove('Category');
+         *     }
+         *
+         * @param SegmentsList $list An instance of the SegmentsList.
+         */
+        Piwik::postEvent('Segment.filterSegments', array($list));
+        
         $cache->save($cacheKey, $list);
 
         return $list;