update CHANGELOG and bump version to 4.0.3

Author: beniwohli

CHANGELOG.md

@@ -1,9 +1,11 @@
 # Changelog
 
-## Unreleased
+## v4.0.3
+[Check the diff](https://github.com/elastic/apm-agent-python/compare/v4.0.2...v4.0.3)
 
  * implemented de-dotting of tag names and context keys (#353)
  * wrote a quickfix for the boto3/botocore instrumentation (#367)
+ * fixed an issue with psycopg2 and encoded strings (#366)
 
 ## v4.0.2
 [Check the diff](https://github.com/elastic/apm-agent-python/compare/v4.0.1...v4.0.2)

elasticapm/version.py

@@ -1,2 +1,2 @@
-__version__ = (4, 0, 2)
+__version__ = (4, 0, 3)
 VERSION = ".".join(map(str, __version__))