chore(java): add a note in README for migrated split repos (#1687) (#921)

* chore(java): add a note in README for migrated split repos

Disable renovate bot and flaky bot for split repositories
that have moved to the Java monorepo.
The Java monorepo will pass the "monorepo=True" parameter
to java.common_templates method in its owlbot.py files so that
the migration note will not appear in the README in the monorepo.

Co-authored-by: Jeff Ching <[email protected]>
Source-Link: googleapis/synthtool@d4b2916
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:edae91ccdd2dded2f572ec341a768ad180305a3e8fbfd93064b28e237d35920a

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

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,4 +13,4 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:821ab7aba89af2c7907e29297bba024d4cd5366d0684e5eb463391cdf4edc9ee
+  digest: sha256:edae91ccdd2dded2f572ec341a768ad180305a3e8fbfd93064b28e237d35920a