update CHANGELOG and bump version to 5.1.0

Author: beniwohli

CHANGELOG.md

@@ -1,7 +1,7 @@
 # Changelog
 
-## Unreleased
-[Check the diff](https://github.com/elastic/apm-agent-python/compare/v5.0.0...master)
+## v5.1.0 
+[Check the diff](https://github.com/elastic/apm-agent-python/compare/v5.0.0...v5.1.0)
 
 ### Security issues
 

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, 0, 0)
+__version__ = (5, 1, 0)
 VERSION = ".".join(map(str, __version__))