fix: make body_template idempotent on whitespace changes

HCL is a superset of json. When providing json data through a heredoc,
terraform interprets it as an actual datastructure (maps / lists, etc)
and jsonencodes it itself.

Providing data like that will result in terraform always showing
whitespace changes like this:

```
~ body_template     = jsonencode( # whitespace changes
      {
          text = "This is a sample json"
      }
  )
```

Use a DiffSuppressFunc to only show changes when there are semantic
differences.

netbox/resource_netbox_webhook.go

@@ -57,6 +57,11 @@ func resourceNetboxWebhook() *schema.Resource {
 			"body_template": {
 				Type:     schema.TypeString,
 				Optional: true,
+				DiffSuppressFunc: func(k, oldValue, newValue string, d *schema.ResourceData) bool {
+					equal, _ := jsonSemanticCompare(oldValue, newValue)
+					return equal
+				},
+				DiffSuppressOnRefresh: true,
 			},
 			"http_method": {
 				Type:         schema.TypeString,

netbox/resource_netbox_webhook_test.go

@@ -87,7 +87,9 @@ resource "netbox_webhook" "test" {
 	trigger_on_delete = "%s"
 	payload_url       = "%s"
 	content_types     = ["%s"]
-	body_template     = "{\"text\": \"This is a sample json\"}"
+	body_template        = <<-EOT
+	{"text": "This is a sample json"}
+	EOT
         http_method       = "%s"
         http_content_type = "%s"
   }`, testName, testEnabled, triggerOnCreate, triggerOnUpdate, triggerOnDelete, testPayloadURL, testContentType, testHTTPMethod, testHTTPContentType),
@@ -115,7 +117,9 @@ resource "netbox_webhook" "test" {
   trigger_on_delete    = "%s"
   payload_url          = "%s"
   content_types        = ["%s", "%s"]
-  body_template        = "{\"text\": \"This is a sample json\"}"
+  body_template        = <<-EOT
+  {"text": "This is a sample json"}
+  EOT
 }`, testName, testEnabled, triggerOnCreate, triggerOnUpdate, triggerOnDelete, testPayloadURL, testContentType, testContentType1),
 				Check: resource.ComposeTestCheckFunc(
 					resource.TestCheckResourceAttr("netbox_webhook.test", "name", testName+"_updated"),