PLT-6358: Server HTTP client improvements (#6980)

* restrict untrusted, internal http connections by default

* command test fix

* more test fixes

* change setting from toggle to whitelist

* requested ui changes

* add isdefault diagnostic

* fix tests

api4/command_test.go

@@ -388,10 +388,13 @@ func TestExecuteCommand(t *testing.T) {
 	channel := th.BasicChannel
 
 	enableCommands := *utils.Cfg.ServiceSettings.EnableCommands
+	allowedInternalConnections := *utils.Cfg.ServiceSettings.AllowedUntrustedInternalConnections
 	defer func() {
 		utils.Cfg.ServiceSettings.EnableCommands = &enableCommands
+		utils.Cfg.ServiceSettings.AllowedUntrustedInternalConnections = &allowedInternalConnections
 	}()
 	*utils.Cfg.ServiceSettings.EnableCommands = true
+	*utils.Cfg.ServiceSettings.AllowedUntrustedInternalConnections = "localhost"
 
 	postCmd := &model.Command{
 		CreatorId: th.BasicUser.Id,