feature flag to increase the timeout for fetching validators

🎯 Problem to be solved

Validator client requests are timing out when requesting a large number of validators, causing errors and preventing validator activation.

[ ] Add a feature flag or configuration option to increase the timeout for fetching validators when the number of requested validators is large (e.g. >200)
[ ] Test this change locally with Kurtosis and with a lighthouse/lodestar setup to ensure block production is not impacted
[ ] Once tested and verified, push the change to the next RC