This commit fixes mixedCluster and rolling upgrades by spoofing OpenSearch
version 1.0.0 as Legacy version 7.10.2. With this commit an OpenSearch 1.x node
can join a legacy (<= 7.10.2) cluster and rolling upgrades work as expected.
Mixed clusters will not work beyond the duration of the upgrade since shards
cannot be replicated from upgraded nodes to nodes running older versions.
Signed-off-by: Nicholas Walter Knize <nknize@apache.org>
Co-authored-by: Shweta Thareja <tharejas@amazon.com>