Consider supporting the last two versions of each runtime in the latest images

[dls314]

Describe the bug
The aws/codebuild/standard:6.0 image only supports the latest version of each runtime; this means that upgrading a CodeBuild job to this image version has to be done in lock-step with upgrading the project buildspec.yml files and project source files. It would be far nicer to have support that overlaps older images so that upgrades can be staggered and don't have to be done in lock-step.

Additional context
The lock-step hits me when asking infrastructure teams to maintain CodeBuild/CodePipeline definitions used by development teams. Development teams using NodeJS 14 have to plan closely coordinated work with infrastructure teams who can't upgrade infrastructure to enable NodeJS 16 without breaking development because there is only one version of the runtime supported in the image.

[lorengordon]

This would be amazing. Python 3.10 isn't even available for Lambda functions. So if I'm using aws/codebuild/standard:6.0, and I want to ensure the lambda is packaged with the same runtime that is going to execute it (to avoid issues with package versions), I have to install the correct python version first. Means the builds are much slower, and its a pretty frustrating user experience overall.

[subinataws]

AWS CodeBuild team member here. Supporting multiple runtime versions within an image led to several sharp edges for our customers. Going forward, we unfortunately can only support a single version of each language runtime in the combined image, which will be the latest supported version at the time of the image release.

[obataku]

I previously brought this up here: #505 (comment)

[dls314]

@subinataws, Any chance that you could describe some of these sharp edges? We found the lack of multiple versions to be quite a problem, honestly.

[lorengordon]

@subinataws I'd also be interested in knowing more about the sharp edges. Support for multiple language runtime versions is very important in any CI runner. Perhaps the implementation just needed some refinement, instead of abandoning it?

[dls314]

Related (essentially duplicate) - #608