Prepare to release 2.1.0 version (#125)

Problem: In order to prepare to the new release Changelog file needs to contain new release section.
Solution: Add a new release section 2.1.0 to the Changelog

CHANGELOG.md

@@ -8,9 +8,6 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Dependencies: updates of dependency versions
 
 ## [Unreleased] - yyyy-mm-dd
-### New features & improvements
-- Add support for Multi-Step API Synthetic Tests
-- Add deprecation warnings for BrowserTest
 
 ### Breaking changes
 
@@ -20,6 +17,14 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ### Dependencies
 
+## [2.1.0] - 2023-09-22
+### Announcements
+- In the future releases some BrowserTest-related methods (test config, variables, etc) will be replaced by the common methods from SyntheticTestBuilder.
+
+### New features & improvements
+- Add support for Multi-Step API Synthetic Tests
+- Add deprecation warnings for BrowserTest
+
 ## [2.0.0] - 2023-09-01
 ### Breaking changes
 - Set target JVM version to 17 ([#106](https://github.com/personio/datadog-synthetic-test-support/pull/106))