[Feature] Slack bot for bridge monitoring

[andygolay]

Create a Slack bot which does the following:

• Periodically post a bridge update into a dedicated Slack channel, e.g. in #bot-layerzero-bridge once per 12 hours initially.
• Bridge update contains:
  • Past 24h bridging volume for ETH, USDC and USDT
  • Current bridge endpoints and network
  • Threshold for topping up escrows
• If an escrow account is close to hitting the threshold for topping it up, increase the post frequency. In practice, if the rate limit from L1 to L2 is 25 million MOVE per day, this could mean that once the L2 escrow account drops from 75 million to 50 million MOVE, there's an alert, and from there if it continues to drop to 40 million MOVE, there's another alert, and so on.
• The bot must monitor the status of escrow accounts frequently, e.g., every 10 minutes, but only send frequent alerts to the channel when it is necessary to top up escrow accounts.

[andygolay]

This has been implemented via 1406702

Todo: containerize and deploy to EC2 instance.