Reduce some EE and builder related ERRO logs to WARN (#3966)

## Issue Addressed

NA

## Proposed Changes

Our `ERRO` stream has been rather noisy since the merge due to some unexpected behaviours of builders and EEs. Now that we've been running post-merge for a while, I think we can drop some of these `ERRO` to `WARN` so we're not "crying wolf".

The modified logs are:

#### `ERRO Execution engine call failed`

I'm seeing this quite frequently on Geth nodes. They seem to timeout when they're busy and it rarely indicates a serious issue. We also have logging across block import, fork choice updating and payload production that raise `ERRO` or `CRIT` when the EE times out, so I think we're not at risk of silencing actual issues.

#### `ERRO "Builder failed to reveal payload"`

In #3775 we reduced this log from `CRIT` to `ERRO` since it's common for builders to fail to reveal the block to the producer directly whilst still broadcasting it to the networ. I think it's worth dropping this to `WARN` since it's rarely interesting.

I elected to stay with `WARN` since I really do wish builders would fulfill their API promises by returning the block to us. Perhaps I'm just being pedantic here, I could be convinced otherwise.

#### `ERRO "Relay error when registering validator(s)"`

It seems like builders and/or mev-boost struggle to handle heavy loads of validator registrations. I haven't observed issues with validators not actually being registered, but I see timeouts on these endpoints many times a day. It doesn't seem like this `ERRO` is worth it.

#### `ERRO Error fetching block for peer     ExecutionLayerErrorPayloadReconstruction`

This means we failed to respond to a peer on the P2P network with a block they requested because of an error in the `execution_layer`. It's very common to see timeouts or incomplete responses on this endpoint whilst the EE is busy and I don't think it's important enough for an `ERRO`. As long as the peer count stays high, I don't think the user needs to be actively concerned about how we're responding to peers.

## Additional Info

NA

beacon_node/execution_layer/src/lib.rs

@@ -1575,10 +1575,10 @@ impl<T: EthSpec> ExecutionLayer<T> {
                         &metrics::EXECUTION_LAYER_BUILDER_REVEAL_PAYLOAD_OUTCOME,
                         &[metrics::FAILURE],
                     );
-                    error!(
+                    warn!(
                         self.log(),
                         "Builder failed to reveal payload";
-                        "info" => "this relay failure may cause a missed proposal",
+                        "info" => "this is common behaviour for some builders and may not indicate an issue",
                         "error" => ?e,
                         "relay_response_ms" => duration.as_millis(),
                         "block_root" => ?block_root,