chore(python): configure release-please on previous major versions (#80)

Source-Link: googleapis/synthtool@c1dd87e
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:2d13c2172a5d6129c861edaa48b60ead15aeaf58aa75e02d870c4cbdfa63aaba

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

packages/google-cloud-datastream/.github/.OwlBot.lock.yaml

@@ -13,4 +13,4 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:4e1991042fe54b991db9ca17c8fb386e61b22fe4d1472a568bf0fcac85dcf5d3
+  digest: sha256:2d13c2172a5d6129c861edaa48b60ead15aeaf58aa75e02d870c4cbdfa63aaba

packages/google-cloud-datastream/.github/release-please.yml

@@ -1,2 +1,8 @@
 releaseType: python
 handleGHRelease: true
+# NOTE: this section is generated by synthtool.languages.python
+# See https://github.com/googleapis/synthtool/blob/master/synthtool/languages/python.py
+branches:
+- branch: v0
+  handleGHRelease: true
+  releaseType: python