[BUG] Replication plugin doesn't apply multi-field mapping update at the follower

[saikaranam-amazon]

What is the bug?
Replication plugin doesn't apply mapping updates at the follower index for the multi-fields mapping update on the leader index.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Have dummy mapping defined for the leader index.
2. Start replication on this index at the follower.
3. update the mapping for the single field at the leader index with additional fields for multi-field update

PUT /<index>/_mapping
{
 "properties": {
   "field1": {
     "type": "text",
      "fields" : {
         "field2" : {
             "type" : "text",
             "analyzer" : "standard"
           },
           "field3" : {
             "type" : "text",
             "analyzer" : "standard"
           }
       }
    }
  }
}

4. Index more docs at the leader index.
5. Notice that the docs are replayed at the follower but mapping update is not performed on the follower

What is the expected behavior?
Even for multi-fields mapping update should be performed.

[sricharanvuppu]

backported to all branches, closing the issue