Allow including templates from source during PR builds

[TimHess]

• separate build and deploy as unique jobs (so we can re-run deployment to staging after a stage/prod swap)
• update action versions
• align styles with other Steeltoe GH Actions
• alter the GitHub actions and dockerfile to add support for including templates built from source code rather than nuget.org.

Use the syntax below for specifying what should be checked out:

template_checkout_target=update-for-Steeltoe-v4

[github-actions]

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[bart-vmware]

I haven't looked deeply in how this all works, but I trust you figured it out.