Do I need to enable "multicast-routing" on ASA inorder to allow IGMPv2 traffic from inside to outside.?
Or just need to enable inspect ip-options ..
To configure ASA as a IGMP proxy agent (without fully participating in multicast routing just to forward IGMP message):
You need to enable multicast routing and configure igmp forward interafce.
Well, that depends,
I mean if all you want is your ASA to be a "proxy" for those sessions you only need the IGMP Stub configuration on the ASA,
Multicast-routing will enable PIM Sparse mode on all of the interfaces as soon as you set the command, so if you do not want the ASA to participate (be another multicast hop in the network) then do not configure it the command and use the stub feature,
Hope I did help here
Usually mcast traffic is UDP-based. Even though the ASA inspection engine inspects UDP by default when going from higher to lower (inside to outside, for example), mcast traffic is vast majority of the time unidirectional.
So depending on your mcast source placement you may need to open a few ports to permit that traffic.