Add support for provisioned deployment model

For the file transfer based rebalance feature, GSI client would need to enable some settings for provisioned deployment models only. 

Currently, query supports setting only serverless deployment model. The code in query/datastore/couchbase/couchbase.go supports the following method:
 

func SetServerless(serverless bool) {

    if serverless {

        cb.SetConnectionPoolParams(_SERVERLESS_CONN, _OVERFLOW_CONN)

        cb.EnableAsynchronousCloser(true, _SERVERLESS_TIMEOUT)

    }

    gsi.SetDeploymentModel(serverless)

    ftsclient.SetDeploymentModel(serverless)

}

The SetDeploymentModel() method accepts "serverless" argument as boolean.

Ask for this MB:

a. Instead of accepting "serverless" argument as bool, accept model as string

b. The value of the argument will be "default" for default deployment model, "serverless" for serverless deployment model, "provisioned" for provisioned deployment model.

GSI side change: https://review.couchbase.org/c/indexing/+/197789