Add `chain_id_caip` jproperty to segment events

This issues supersedes https://github.com/MetaMask/MetaMask-planning/issues/1840

New plan is to set `chain_id: null` for chains that don't have a hexidecimal `chain_id` (like bitcoin, solana, etc), and set `chain_id_caip` to their respective CAIP2 chain ids instead.

For ethereum-like chains (chains with a hexidecimal chain_id) we'll need to send both `chain_id` and `chain_id_caip`.

We'll likely need additional information and details, as the issue this issue replaces has a couple of other changes it proposes that need to be confirmed (as its been a while since that issue was updated).

Review the superseded planning issue at https://github.com/MetaMask/MetaMask-planning/issues/1840 and confirm which additional changes still apply. Done means segment events send chain_id_caip for all chains, use null chain_id for non-hexadecimal chain IDs, and send both fields for Ethereum-like chains.

Written by the indexing model from the issue text.