Add Note about dropping go 1.18 (#3771)

* Add Note about dropping go 1.18

* Fix lint

* Apply suggestions from code review

Co-authored-by: Robert Pająk <pellared@hotmail.com>

---------

Co-authored-by: Damien Mathieu <damien.mathieu@elastic.co>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Robert Pająk <pellared@hotmail.com>

CHANGELOG.md

@@ -8,6 +8,9 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+This release is the last to support Go 1.18.
+The next release will require at least Go 1.19.
+
 ### Added
 
 - Semantic conventions of the `event` type are now generated. (#3697)