Make the engine get blobs method required

[mehdi-aouadi]

The current implementation of the engine_getBlobsV1 is marked as non critical and doesn't trigger an EL status update (in DefaultExecutionWeb3jClientProvider::buildClient) since it hasn't been implemented by all the ELs yet.
This should be removed from the non critical methods once it's implemented widely.
The required change:
Remove engine_getBlobsV1 from DefaultExecutionWeb3jClientProvider::buildClient

A new notion of optional execution RPC methods has also been added to handle the use case when an EL doesn't support the new method. This should be removed once all ELs have implemented it.
The required change:
Remove isOptional from EngineJsonRpcMethod
Remove MilestoneBasedEngineJsonRpcMethodsResolver::getOptionalCapabilities
Remove optionalCapabilitiesSupplier from EngineCapabilitiesMonitor

[tbenr]

Regarding nonCritical, I think we should leave that method in the list.
Imagine a CL client has a bug only on engine_getBlobs: we can still work nicely.
Marking the EL as offline as a "critical" method, IIRC, has downstream affects on our overall availability.