[docs] dynamically read chain list from latest registry instead of the registry package

[avious00]

• Address & Domains should reflect the updated registry
• Have the chain dropdown component (which I believe pulls from the AddressTable) e.g. in Send Your First Message & Post-Dispatch Hooks reflect the registry's chain list

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1. Restrict Send your first message addresses to Ethereum #174
   docs dx +2
   

[jmrossy]

@avious00 This was already partly done here: #79
But it uses the static info in the published registry instead of dynamically querying, meaning the registry version in this repo must be regularly updated. We can make this dynamic but we should do hyperlane-xyz/hyperlane-registry#42 first