The primary shards of follower indices during the bootstrap need to be
on nodes with the remote cluster client role as those nodes reach out to
the corresponding leader shards on the remote cluster to copy Lucene
segment files and renew the retention leases. This commit introduces a
new allocation decider that ensures bootstrapping follower primaries are
allocated to nodes with the remote cluster client role.
Co-authored-by: Jason Tedor <jason@tedor.me>
4d7c59bedb