update CHANGELOG and bump version to 5.3.0

Author: basepi

CHANGELOG.md

@@ -1,7 +1,7 @@
 # Changelog
 
-## Unreleased
-[Check the diff](https://github.com/elastic/apm-agent-python/compare/v5.2.3...master)
+## v5.3.0
+[Check the diff](https://github.com/elastic/apm-agent-python/compare/v5.2.3...v5.3.0)
 
 ### New Features
 

elasticapm/version.py

@@ -28,5 +28,5 @@
 #  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 #  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-__version__ = (5, 2, 3)
+__version__ = (5, 3, 0)
 VERSION = ".".join(map(str, __version__))