Ability to pass launchpad config using stdin

[surskitt]

It would be very useful to be able to pass the launchpad yaml config into the command through standard in, for example when taking input from a computed source like terraform outputs. Instead of having to write to file, we could do something like below:

terraform output launchpad_yaml | launchpad apply -c -

[kke]

Yep, I've been thinking about this too. Now that the terraform examples output yaml it makes even more sense. I've made the change and this will be available in version 1.1.