Adding Generic Template Handler

[bfoley13]

Description

This is the addition of the generic template handler, some template definition validation, and some documentation. This will not block/break any existing template/cli logic as it does not integrate it yet

Next steps in the next PR will be to:

• Update all templates to using Draftconfig within the templates
• Migrate old handlers(deployments/workflows/dockerfiles/etc.) to use generic template handler
• Add test logic to the generic template handler. Cant do this yet as we have no template definitions that are migrated.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Refactor

How Has This Been Tested?

Provide instructions so we can reproduce, and list any relevant details for your test configuration. Please mention if this is a breaking change which will impact consuming tool(s).

• Unit Test:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[jaiveerk]

lgtm for the most part just a few suggestions

[davidgamero]

lgtm