Add executionPayload abstraction in PayloadTypes

[mattsse]

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Describe the feature

currently we have hardcoded the executionpayload type and sidecar:

https://github.com/paradigmxyz/reth/blob/3408059393bcf03f6727f790ec52f28114e25d02/crates/engine/primitives/src/message.rs#L144-L148

ideally we want this to be configurable.

especially when we want to make custom block types work.

first step would be introducing an associated in the EngineTypes

https://github.com/paradigmxyz/reth/blob/3408059393bcf03f6727f790ec52f28114e25d02/crates/engine/primitives/src/lib.rs#L33-L33

that encapsulates both, for example type ExecutionPayloadRequest

and add a helper type that has the payload and sidecar as fields

Additional context

No response