[Request] Hide env variables that are secrets

[sergioisidoro]

Using env variables for secrets is a quite common scenario, and a lot of PaaS use that (eg. Heroku)
However it is also a quite common situation that secrets are not readable after they are set (eg. they appear as Hu**********)

It would be nice if we could have a checkbox on the env variables to mark something as a secret, so that it wouldn't be readable from the UI after it is set.

If CapRover stores these env as a plain file, this might be problematic, but if this is stored in any other format (they seem to be stored in app.envVars), which is able to store metadata, it would be nice.

eg: