Improve Add Policy API by using transport action instead of timeout

[qreshi]

The initial implementation of the Add Policy API had a concerning case where two requests to add policy could overwrite each other. The concern was brought up here.

As a temporary fix, a timeout of 30 seconds was added to the Add Policy API action. As a more permanent fix, a transport action should perform the logic of iterating through the cluster state and updating the indices' settings on the master node itself, preventing requests to add policy both returning 200 status and one overwriting the other.