Related:#6100

This PR extends the rich parameters feature to let users mark them as optional. This behavior is consistent with Terraform variables.

A rich parameter is consideredrequired when it doesn't contain thedefault property, so:

data"coder_parameter""another_required_field" {name="Another required field"icon="/icon/aws.png"description="This string is required"mutable=true}

If we want to mark the parameter as optional, we need to add thedefault property:

data"coder_parameter""random_string" {name="Optional random string"icon="/icon/aws.png"description="This string is optional"mutable=truedefault=""}

Changes:

• use the latest terraform-provider-coder to support computed property "optional" (not exposed to users)
• adjust coderd API to exposerequired property
• site: allow for empty, optional parameters
• site: use HTML API to check if field is required
• modify CLI to allow for entering values for newly added parameters to templates

Follow-ups:

• present a special form or popup to enter required params without defaults (especially if those are new parameters)