[Remote Store] Fix message on enabling remote store without segment replication

[sachinpkale]

Describe the bug

• Currently, if we try to enable index.remote_store.enabled without setting replication type to SEGMENT, we get following error:

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Settings index.remote_store.enabled cannot be enabled when index.replication.type is set to DOCUMENT"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "Settings index.remote_store.enabled cannot be enabled when index.replication.type is set to DOCUMENT"
  },
  "status" : 400
}

• But this does not make the dependency of segment replication clear. With this change, we are changing the error message to:

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "To enable index.remote_store.enabled, index.replication.type should be set to SEGMENT"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "To enable index.remote_store.enabled, index.replication.type should be set to SEGMENT"
  },
  "status" : 400
}