Monitor deployments again

[maximlt]

A few months ago we migrated our deployment solution Anaconda Workbench from Digital Ocean to AWS. This came with some difficulties that are still being worked out, leading to the deployments being currently unstable. At the moment, we have pretty much no monitoring in place. We need to re-enable monitoring when the deployments become more stable.

• Re-enable the lambda checking deployments
  The static site now hosts a JSON file that lists the expected deployments, it could be used to feed the lamba: https://examples.holoviz.org/_static/deployments.json
• Document the lambda, for now I suggest in a file on the repo that is not part of the website
• Add a doit task that reports the state of all the deployments (same code as the lambda basically)
• I'd love it if we could host a static page / tiny Panel app that reports the status of each deployment when visited.

(I chose not to comment in #184 that has a similar goal but is a bit outdated)

[maximlt]

#426