Missing spec values at `/eth/v1/config/spec`
**Describe the bug**

Hey team, I'm running a local Pectra devnet to make sure our VC ([Vero](https://github.com/serenita-org/vero)) is ready for the upgrade and noticed Nimbus doesn't return some spec values, specifically:
`MAX_DEPOSIT_REQUESTS_PER_PAYLOAD`, `MAX_ATTESTER_SLASHINGS_ELECTRA`, `MAX_WITHDRAWAL_REQUESTS_PER_PAYLOAD`, `MAX_CONSOLIDATION_REQUESTS_PER_PAYLOAD`, `MAX_ATTESTATIONS_ELECTRA`.

The validator client has its own hardcoded specs but on launch it attempts to verify its spec matches with the connected beacon node's spec.

**To Reproduce**
Steps to reproduce the behavior:
1. Platform details (OS, architecture): 'N/A'
2. Branch/commit used: I used the latest `ethpandaops/nimbus-eth2:unstable` image (as posted in the #interop channel on Discord)
3. Commands being executed: `nimbus_beacon_node --non-interactive=true [...]` (standard Kurtosis config for Nimbus CL)
4. Relevant log lines: 'N/A'

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**Additional context**
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