parameters generate command should allow using default values

[carolynvs]

When a parameter has a default value defined, we should allow skipping setting that parameter in the parameter set so that they can use the default value.

Example

$ porter parameters generate hello-llama --reference getporter/hello-llama:v0.1.1
Generating new parameter set hello-llama from bundle hello-llama
==> 2 parameters declared for bundle hello-llama

? How would you like to set parameter "name"
   [Use arrows to move, space to select, type to filter]
  secret
  specific value
  environment variable
  file path
  shell command
> use default value (DEFAULT VALUE)

[divbhasin]

I would like to work on this :) Did some digging and I think I know what changes need to be made. Just wanted to clarify that the "default" value for a param refers to the following result of running porter explain on hello-llama:

[carolynvs]

Yup! That is the default value used for the parameter when the user does not specify it. 👍

[kichristensen]

Implemented with a skip option in #3100