add Pod that would validate payment globally, independant of graphql/mongodb

[nicolasburtey]

the idea would be that the pod:

• would be a proxy between graphql and lnd,
• would be the only one with write access to payment function on lnd
• would enforce global security rules. :

like: if there are more than 20m sats leaving the app in the last 6 hours, pause payment and trigger an alert for further investigation.

this pod could be isolated from graphql / mongodb, which has a pretty big attack surface given it's the app that received all the requests from clients.

[nicolasburtey]

this would be a good API to do it once it's merge in the master branch of lnd: lightningnetwork/lnd#5101