Lambda support for Python servers (#1807)

* Allow running Python servers with Lambda handler

* Fix doctests

* Add `Running servers on AWS Lambda` section to docs

* Remove empty spaces from `README` to make linter happy

* Rename `run_lambda_server` to `run_lambda_handler`

* Add more comments to example `Dockerfile`

* Fix capitalization of logs

* Preserve original formatting of `PythonApplicationGenerator.kt`