Extracted from:#5574

Blockers:

• rich parameters: Manage template-wide Terraformvariable #5980
• rich parameters: user environment variable input #5981
• docs: rich parameters #6074
• rich parameters: convert Coder examples #6073

The goal of this issue is to deprecate and remove old parameters in favor of rich parameters.

To be reviewed and adjusted:

• CLI
• site/UI
• Coder API
• Database model

Once this issue is resolved, it won't be possible to use templates with old parameters, and all relevant workspaces must be switched to templates with rich parameters.