Additional Runtime APIs and RPC Methods

[mustermeiszer]

This is a tracking issue for additional runtime apis we want to provide and the respective rpc methods if those methods should be exposed to the outer world.

In most cases, we will want both API & rpc as we have no real need for runtime apis that only the node internally uses currently. (Might change once we have ZKPs for which nodes need to access the runtime).

APIs & RPC

• RtApi - PoolValuation RuntimeApi and RPC Method #750
• TokenPrice RuntimeApi and RPC Method #749
• EpochSolution Inspection RuntimeApi and RPC Method #748
• Pools Data: Retrieving tranche ids from indexes,
• RtApi - Max borrow amount #793