feat: Improve filter validation to show error on misconfiguration

[alexluong]

Improving the filter validation so that if users have a wrong TF resource configuration we'll throw an error. For example:

resource "hookdeck_connection" "connection_example" {
  source_id      = hookdeck_source.example.id
  destination_id = hookdeck_destination.destination_example.id
  name           = "my-connection"
  rules = [
    {
      filter_rule = {
        body = {
          hello = "world"
        }
      }
    }
  ]
}

will result in this error

│ Error: Invalid Attribute Type
│
│   with hookdeck_connection.connection_example,
│   on main.tf line 52, in resource "hookdeck_connection" "connection_example":
│   52: resource "hookdeck_connection" "connection_example" {
│
│ Attribute rules[0].filter_rule.body value must have exactly one child attribute defined, got:
│ {"boolean":<null>,"json":<null>,"number":<null>,"string":<null>}