MDL-83361 reportbuilder: date aggregation for timestamp columns.

This change introduces updates to the existing aggregation API, to
allow types to define whether to group by fields of a column to which
the aggregation is applied.

The new date aggregation utilises this, to allow for creation of time
series reports, e.g. report data grouped by dates.

Co-authored-by: Daniel Neis Araujo <danielneis@gmail.com>

.upgradenotes/MDL-83361-2024101618221379.yml

@@ -0,0 +1,12 @@
+issueNumber: MDL-83361
+notes:
+  core_reportbuilder:
+    - message: >-
+        The base aggregation class has a new `column_groupby` method, to be
+        implemented in aggregation types to determime whether report tables
+        should group by the fields of the aggregated column
+      type: improved
+    - message: >-
+        There is a new `date` aggregation type, that can be applied in custom
+        and system reports
+      type: improved