Use hardened containers

[dandersonsw]

Changes proposed in this pull request:

• Updates the pipeline to use currently available hardened images
• Simplifies the pipeline code by creating a resource for the general-task image and referencing that resource using the image key rather than needing to specify it in every yml file
• Updates yml files so they are all formatted the same

Things to check

• For any logging statements, is there any chance that they could be logging sensitive data?
• Are log statements using a logging library with a logging level set? Setting a logging level means that log statements "below" that level will not be written to the output. For example, if the logging level is set to INFO and debugging statements are written with log.debug or similar, then they won't be written to the otput, which can prevent unintentional leaks of sensitive data.

Security considerations

Updates the pipeline to use hardened images, including updating the built-in resources with our own hardened resource images

[jameshochadel]

Besides one comment this looks great. Nice job factoring out the image fields. Thanks!

[jameshochadel]

Although it'll mess up the alphabetical order, let's put this one first so all subsequent images are pulled using our version of registry-image. If you want, you could link to this explanation, but totally up to you: https://github.com/cloud-gov/container-scanning/blob/main/docs/harden-pipelines.md#implementation

[dandersonsw]

Updated the order, thanks James!