Add new RPC endpoints to support Beacon network data

[acolytec3]

We should some higher level endpoints to the RPC for things like beacon_getLightClientUpdate and beacon_getBootstrap and maybe beacon_lightClientStatus to allow visibility into how our embedded light client is doing (i.e. is it tracking the head of the chain, etc).

[acolytec3]

@holgerd77 I'm guessing this question is related to this tracking issue maybe? If so, then this is specifically the lodestar light client and not the full beacon client. It's quite light weight but it runs inside of Ultralight and essentially just listens for beacon light client data objects that are gossiped over the portal network and updates its own internal state when it finds things its looking for (i.e. light client updates and optimistic updates).

[holgerd77]

Haha, yes.

[acolytec3]

Have added:

• beacon_getHead - returns the capella fork Light Client Header corresponding to the current known head block
• beacon_getFinalized - returns the capella fork Light Client Header corresponding to the current known Finalized block

[acolytec3]

Added beacon_getLightClientUpdate was added in #530

[acolytec3]

This PR documents all the official beacon RPC endpoints we should implement. I think we have most of them already but should confirm against this list.

[acolytec3]

We're missing quite a few after referencing the list above. But, we're missing lots of endpoints all around, the entire trace sub-namespace is missing so we should think about implementing some of these.