support a new build type for components with no artifacts

[massi-ang]

Describe the bug
I have a component with no artifacts, just a recipe. When I use gdk component publish, the command fails saying

[Errno 2] No such file or directory: '/Users/xxx/Projects/comp/greengrass-build/recipes/recipe.yaml'

To Reproduce
Steps to reproduce the behavior. If possible, provide a minimal amount of code that causes the bug.

Create a compoent with only a recipe, no artifacts. In the gdk-config.json file, provide a noop custom build command (eg date) so the gdk component build succeeds.

Call gdk component publish

Expected behavior
A clear and concise description of what you expected to happen.

Component is successfully published

Actual behavior
Tell us what actually happened.

Error

[Errno 2] No such file or directory: '/Users/xxx/Projects/comp/greengrass-build/recipes/recipe.yaml'

Environment

• OS: [e.g. Ubuntu 20.04] (If possible, provide output of uname -a)
• JDK version:
• Nucleus version:

Additional context
Add any other context about the problem here.

E.g. what is the impact of the bug?

[saranyailla]

Hi,
This is the expected behavior and thank you for reporting this use case.
If the customer chooses custom build in the config file, we expect customers to modify/build the recipes and artifacts as needed and have them available in the greengrass-build folder by the end of the build command execution.

These will later be used by the publish command.

I'm going to re-label this as documentation as it is needs to be specified in the documentation explicitly.

Edit:
Since, having only recipes with no artifacts for a component is a common use case, we decided to actively track the support for it.

[saranyailla]

Hi,
AWS Public Documentation for GDK CLI is updated with more details related to custom build command.

[atcollins06]

Would like to add another voice to request support for a recipe only build type. Every user shouldn't have to write their own program to do the substitution into the recipe file, especially when the gdk code base already has the capability to do it.