Add MailChain Module

[kamescg]

As a Developer I want to allow my users to easily share encrypted messages with each other.

Add MailChain so "people can communicate using their Web3 identities, such as ENS names, through a private, end-to-end encrypted mail experience."

Resources:

• https://mailchain.notion.site/ETH-Denver-Hack-Pack-2023-51e6bc0070c448118f34c39fd673934b
• https://github.com/mailchain/docs/blob/main/docs/developer/tutorials/integrations/tenderly-on-chain-event-notifications.md
• https://twitter.com/MishaDV_/status/1634913483849334784