fix: silence home directory warning when running on lambda (#893)

* fix: silence home directory warning when running on lambda
update: SDK_CHANGELOG.md

* update: expand_home to take env
update: tests broken by expand_home change
fix: check correct env in check_is_likely_running_on_a_lambda
add: test load_config_file_should_not_emit_warning_on_lambda

* update: check LAMBDA_TASK_ROOT instead of AWS_EXECUTION_ENV