Add a 'set replica identity' operation

[andrew-farries]

Add support for a new set replica identity operation type. The new operation looks like this:

{
  "name": "29_set_replica_identity",
  "operations": [
    {
      "set_replica_identity": {
        "table": "fruits",
        "identity": {
          "type": "full"
        }
      }
    }
  ]
}

This sets the replica identity for the fruits table to FULL. The other supported operation types are 'nothing', 'default', and 'index'. If the replica identity is being set to an index, the operation looks like:

{
  "name": "29_set_replica_identity",
  "operations": [
    {
      "set_replica_identity": {
        "table": "fruits",
        "identity": {
          "type": "index",
          "index": "some_index_name"
        }
      }
    }
  ]
}

The replica identity is set directly on the underlying table on operation start. This means that both versions of the table exposed in the new and old versioned views will have the new replica identity set.

The docs have been updated with the details of the new operation here.