New `pr_build.yaml`.

[jsfillman]

Updated pr_build.yaml to utilize our new reusable workflows:

• All jobs now utilize reusable workflows, located in this repo's .github/workflows directory.
• Opening/updating PRs to develop cause an image to be built for test, but not pushed.
  • This reduces confusion and excessive images.
• Merging PRs to develop causes a new image to be built, pushed, tagged as both PR-## and latest as {APPNAME}-develop.
  • This solves issue with failed tagging, when a PR was merged before original build completes, and reduces tags.
• Opening/updating PRs to main or master causes an image to be built and immediately pushed with the PR-## tag to {APPNAME}
• Merging PRs to main or master causes an image to be built, pushed, and tagged as both PR-## and latest-rc as {APPNAME}.
  • This reduces confusion between merged pre-release PRs and images built with the release workflow.
• All jobs are included in one single file for easy addition via Actions > New workflow, but skipped jobs are very clear and obvious.

[jsfillman]

To see this in action, and the resulting images, check out https://github.com/kbase/actions_test_repo2