Build missing yaml message

[kichristensen]

What does this change

Provides are more user-friendly error message when running porter build from a directory not containing porter.yaml.

Previously the error message looked like this:

$ porter build
unable to read manifest file : could not read the manifest at "": read ~/unclear-message: is a directory
unable to generate manifest: unable to read manifest file : could not read the manifest at "": read ~/unclear-message: is a directory

With this change it looks like this:

$ porter build
could not find porter.yaml in the current directory ~/unclear-message, make sure you are in the right directory or specify the porter manifest with --file

What issue does it fix

Closes #2926 and closes #2991

Notes for the reviewer

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our [Contributors][contributors] list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR

[kichristensen]

@schristoff Sorry about the failing tests, it has been fixed now

[schristoff]

Thank you so much and congrats on your first contribution!!! 🎉💃