CloudFormation template for managing the project's AWS CodeBuild workflows

[bmoffatt]

Description of changes:

~~Validating #154 threw me down a rabbit hole of regression testing. The biggest change I made was to resolve constantly waiting for AWS SDK build, by moving the step out of any ci/codebuild/*.yml and into the respective ci/docker/* - to cache it for personal sanity.~~ moved to #162 - This PR focuses now only on codifying the existing AWS CodeBuild CI workflows into a CloudFormation template

Adds:

• ~~CI support for ArchLinux ci/docker/arch-linux ci/codebuild/arch-linux.yml~~ moved to #161
• CloudFormation template ci/codebuild.yml to model the AWS Code Build resources
• helper script ci/update-images.sh for re-building and re-uploading the ci/docker/* images
• ~~instructions to CONTRIBUTING.md for guidance on executing the CodeBuild testing locally based on https://docs.aws.amazon.com/codebuild/latest/userguide/use-codebuild-agent.html~~ moved to #160

This PR is for visibility - I am expecting some of the existing workflows to break, ~~and need still need to synthesize the new CodeBuild project resources into the account used for this project before the web hooks take effect~~ (edit: I have deployed this stack, web hooks can be seen in this PR and other recent PRs). Testing of the new workflows was initially done by synthesizing into a separate account, and setting the target repository to the fork/branch this PR is based on.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[marcomagdy]

I love the changes. Thank you for doing all that work. Would it be too much to ask to split this PR into many smaller ones? perhaps one that achieves each of the bullet points you outlined? it would make it a lot easier to review/digest.

[bmoffatt]

Can do!

[bmoffatt]

split out the other changes, and will get around later to updating this PR to focus only on ci/codebuild.yml and ci/update-images.sh