Configure 0 replicas for system indexes for single-node clusters

[AWSHurneyt]

Currently, .opendistro-alerting-alert-history indexes always have 1 replica shard, even for single-node domains. This causes those domains to always be yellow.

Consider adjusting the sharding strategy for all system indexes to align with the per document monitor queries indexes such that SETTING_AUTO_EXPAND_REPLICAS would be set to 0-1.
https://github.com/opensearch-project/alerting/pull/1702/files#diff-e7296dbf89637cdb1421bf2be399a263f94b49f0a1280e2e75ef755deeafe075R135

Pros

• This would allow single-node clusters to become green.

Cons

• No replicas would be available for single-node clusters in situations when primary shards are lost.

[AWSHurneyt]

For context, the security plugin also uses similar a sharding strategy for its system indexes
opensearch-project/security#5030