chore: set up release-please for previous major version (1.x) (#1535)

* chore: configure CI for 1.x branch (#1528)

* chore: set up release-please for previous major version (1.x)

* revert owlbot.py change as it already excludes release-please.yml

* chore: set up release-please for previous major version (1.x)

* revert owlbot.py change as it already excludes release-please.yml

* Revert "chore: configure CI for 1.x branch (#1528)"

This reverts commit 54e63ea.

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

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

Author: shobsi

.github/release-please.yml

@@ -3,3 +3,8 @@ handleGHRelease: true
 extraFiles:
   - bigframes/version.py
   - third_party/bigframes_vendored/version.py
+
+branches:
+  - branch: v1
+    handleGHRelease: true
+    releaseType: python