Spelling relayChain and paraId not accepted by smoldot

[bLd75]

Using latest build of smoldot 0.7.9 doesn't accept fields spelled relayChain and paraId from chain specs, they have to be relay_chain and para_id.

TypeError: Cannot read properties of undefined (reading 'para')

This creates a gap with substrate chain specs format which is confusing for para teams.
This was supposedly accepted in #2366