With parameters being managed by coder_paramater, the variable is free for being only template-wide! We can add a panel in the UI for template admins to edit the variables for templates.

Some notes:

• When edited, this should probably push a new template version
• Make it clear to the user that these are essentially setting TF_VAR_{name}={value} env vars during provision-time
• Allow users to mark some as sensitive, which hides them from build logs (and perhaps the user from retrieving the value after).
• We may also want to consider how this would be updated via CLI/on template push. For example, it would be neat if we could push a new template version that references the SHA of a Docker image that was just built in the pipeline.

This can be used during POCs to set AWS access keys, a "main" repo for every template user to clone, or simply values that an admin would prefer to control with more ease (e.g. base AMI).