Add custom env vars

[lbassin]

Is your feature request related to a problem? Please describe.
I think it may be a good idea to add a field to some containers allowing users to set env vars like database credentials

Describe the solution you'd like
An input in container setup page with multiple line and for each line there is two fields : Key and Value

Ui would look something like this :
|| => || (+)

[cvilleger]

IMHO, mabye not database credentials, but other things like an external API credentials. Sounds great 👍