feat: support list(string) as coder_parameter

[mtojek]

Related: #6582

This PR enables support for list(string) as coder_parameter's type (terraform-provider-coder: 0.6.20). In the follow-up, I will see if CLI requires improvements.

data "coder_parameter" "security_groups" {
  name        = "Security groups"
  icon        = "/icon/aws.png"
  type        = "list(string)"
  description = "Select appropriate security groups."
  mutable     = true
  default     = jsonencode([
    "Web Server Security Group",
    "Database Security Group",
    "Backend Security Group"
  ])
}