Add GetObjectDirectorySize RPC

This RPC will be used to determine if a push will
exceed the size limit of a repository.
4 jobs for pb-get-objects-directory-size in 1 minute and 15 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #224820395
build

00:01:11

passed #224820396
check-grpc-proto-clients

00:01:14

passed #224820397
danger-review

00:00:24

passed #224820394
test

00:01:15