adding release notes

Author: mieslep

RELEASE.md

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+# Release Notes
+
+## [4.0.0] - 2023-06-02
+This release is a major code refactor of Cassandra Data Migrator, focused on internal code structure and organization. 
+Automated testing (both unit and integration) was introduced and incorporated into the build process. It includes all
+features of the previous version, but the properties specified within configuration (.properties) file have been 
+re-organized and renamed; therefore, the configuration file from the previous version will not work with this version.
+
+New features were also introduced with this release, on top of the 3.4.5 version.
+### Added
+- New features:
+    - `Column renaming`: Column names can differ between Origin and Target
+    - `Migrate UDTs across keyspaces`: UDTs can be migrated from Origin to Target, even when the keyspace names differ
+    - `Data Type Conversion`: Some predefined Codecs support type conversion between Origin and Target; custom Codecs can be added
+    - `Separate Writetime and TTL configuration`: Writetime columns can differ from TTL columns
+    - `Subset of columns can be specified with Writetime and TTL`: Not all eligible columns need to be used to compute the origin value
+    - `Automatic RandomPartitioner min/max`: Partition min/max values no longer need to be manually configured
+    - `Populate Target columns with constant values`: New columns can be added to the Target table, and populated with constant values
+    - `Explode Origin Map Column into Target rows`: A Map in Origin can be expanded into multiple rows in Target when the Map key is part of the Target primary key
+
+## [3.x.x] 
+Previous releases of the project have not been documented in this file