Describe the feature
We currently don't support signature aggregation due to gas estimation/attribution issues. Currently nobody would pay for the aggregated signature validation, and the bundler doesn't take this into account when estimating the gas of its bundle.

A potential way to fix this:

• estimateUserOperationGas needs to be aggregator aware
• Rundler maintains a whitelist of signature aggregator contracts
• Each entry encodes a fixed cost + variable cost for each aggregator
• When estimating, we call simulateValidation to get the aggregator_info
• If populated, check whitelist. Not whitelisted, reject. If whitelisted
  • Add fixed_cost / BUNDLE_TARGET + variable_cost to the preVerificationGas
  • BUNDLE_TARGET can be set per aggregator. Bundles smaller than the target: the bundler loses money, bundles larger than the target: the bundler makes money