Automate update to java-shared-config docker image tag

[mpeddada1]

Currently, the docker image tag needs to be updated manually. See #690.

• Verify if <!-- {x-version-update:google-cloud-shared-config:current} --> works on yaml files.

[suztomo]

<!-- is not YAML comment.

"extraFiles" in Release Please may help. https://github.com/googleapis/java-storage/blob/main/.github/release-please.yml#L4 and https://github.com/googleapis/release-please/blob/main/docs/customizing.md#updating-arbitrary-files

[mpeddada1]

Release Please is now set up to automatically update image tags (#733) after changes in #720 and #729