Multiple messages gets send when we send messages directly to large groups.

[pankaj-ag]

From @dlobo

@pankaj Agrawal i think we should obsolete that functionality (for now) or restrict it so that we send to groups < 32 contacts only (or some small number). We should encourage people to use start contact on flows instead
we need to rewrite that code to use a mechanism like broadcast. it currently loops forever sending each contact one at a time (with no upper limit)
and I suspect the front end is waiting and then repeats the call since the first call has not returned. @mohd Shamoon or @kurund can confirm behaviour on this and/or apollo in case of timeout
I recommend we put in a hotfix to disable this if the group size is too big for now
(so change backend only)
we can discuss tomorrow and see what it takes to move @tejas-reapbenefit to use start flow for a group scheme

so here's my suggestion:

1. hotfix backend to not disable functionality for groups > 32 contacts
2. Extend broadcast table to handle 3 cases: start the flow, send session message, send hsm message. Here we'll need to store the message_params and the message type
3. Extend the broadcast_contacts code to handle the latter two cases
   I looked at the code and it seems quite feasible, but I think we should sleep over items 2 and 3 and roll 1 into production soon