Elasticsearch currently blocks writes by default when a master is unavailable. The cluster.no_master_block setting allows
a user to change this behavior to also block reads when a master is unavailable. This PR introduces a way to now also still
allow writes when a master is offline. Writes will continue to work as long as routing table changes are not needed (as
those require the master for consistency), or if dynamic mapping updates are not required (as again, these require the
master for consistency).
Eventually we should switch the default of cluster.no_master_block to this new mode.
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