pubsys: don't require Infra.toml to get started

[tjkirch]

Issue number:

Found by @izaakschroeder in #1162 (issue is unrelated)

Description of changes:

If the user has no Infra.toml, we can continue with defaults most of the time.
For making an AMI, only passing PUBLISH_REGIONS is required.  For making a
repo, we can use a default configuration and write it under 'default'. SSM
still requires Infra.toml.

Testing done:

Tested ami, publish-ami, and repo tasks (and ssm, though it didn't change) with and without an Infra.toml file. They worked as expected:

• With Infra.toml:
  • ami and publish-ami use region from file
  • repo is built in build/repos/default by default
  • ssm works
• Without Infra.toml:
  • ami and publish-ami require -e PUBLISH_REGIONS, and work
  • repo is still built in build/repos/default and that section of my config is detected
  • ssm doesn't work, as expected; prefix is required. (This could be a future improvement, passing through prefix from a variable.)

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[zmrow]

🦓

[izaakschroeder]

Looks fantastic to me! It might be useful to note which things require/don't require the Infra.toml file in your PUBLISHING.md. 🎉

[tjkirch]

It might be useful to note which things require/don't require the Infra.toml file in your PUBLISHING.md.

That's a good point. It's covered for AMIs, where we have the longer command that doesn't rely on Infra.toml in BUILDING.md, and move to a simpler command that relies on Infra.toml in PUBLISHING.md. I guess that's the theme of PUBLISHING.md - we're expecting that most users going through the steps beyond creating an AMI are a bit more invested, and so creating an Infra.toml makes sense. Then again, you seem invested and you're asking for it, so theory disproven I guess :)

[tjkirch]

^ This push adds a couple notes to PUBLISHING.md describing what you can do without an Infra.toml, per @izaakschroeder. (There's already a note in the SSM section that it's required there.)

[izaakschroeder]

Thanks for being so prompt and open to feedback! 😄