chore: Add .repo-metadata.json file for java-core (#9250)

Fixes: #9249 

File is pulled from https://togithub.com/googleapis/java-core/blob/66212871e334db68a3f603aab919ede9d97c56b3/.repo-metadata.json
1 file changed
tree: 36644b4f01b8edd582d5f3c1ad8a93e28bdfc8ea
  1. java-core/