add rest interface with default raw json content type

[jordo]

This adds a by default unwrapped /v2/rest route, which routes to the same RPC endpoints. This was needed by us for some integrations (Xsolla purchsing for one) that need to connect to endpoints with unwrapped application/json content-type requests, but are unable to add the unwrap=X URI parameter.

[CLAassistant]

All committers have signed the CLA.

[BergerBytes]

Just a bystander, but was there a reason this wasn't accepted? Is there anything that needs to be done first?

[jordo]

Yes, this changeset is pretty minimal. ping @novabyte