Implement metadata building for Aggregation ISMs

[tkporter]

Note this should be built out in a protocol agnostic manner, but we expect to only implement chain interactions (view calls, etc) for EVM for now.

In the SDK:

• Implement a metadata builder for an aggregation ISM. See Rust implementation for inspiration and the Solidity library for Aggregation ISM metadata.
  • Pick threshold metas that we were able to successfully build metadata for. Note that we won't be supporting the building of MerkleRootMultisig ISM metadata (because this requires data that's hard to get for self-relaying), and aggregation ISMs often include these. So we should be tolerant of us not being able to build sub module ISM metadata. In the agents, we have some logic to use the cheapest valid metadatas, but this is 100% optional, imo it's fine here to just arbitrarily pick the threshold sub modules that we were able to successfully build metadata for
  • Similar to Implement metadata building for Routing ISMs #3450, we'll need to make sure that we don't recurse infinitely, e.g. that imagine someone configuring an aggregation ISM that points to itself