chore: Add header checker config to python library synth (#138)

Now that we have it working in [python-docs-samples](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/.github/header-checker-lint.yml) we should consider adding it to the 🐍 libraries :)

Source-Author: Leah E. Cole <6719667+leahecole@users.noreply.github.com>
Source-Date: Mon Jan 25 13:24:08 2021 -0800
Source-Repo: googleapis/synthtool
Source-Sha: 573f7655311b553a937f9123bee17bf78497db95
Source-Link: https://github.com/googleapis/synthtool/commit/573f7655311b553a937f9123bee17bf78497db95
2 files changed