PLT-1649: add response_url support for custom slash commands (#6739)

* add response_url support for custom slash commands

* pr suggestions

* pr update / suggestion

* test fix

store/store.go

@@ -41,6 +41,7 @@ type Store interface {
 	System() SystemStore
 	Webhook() WebhookStore
 	Command() CommandStore
+	CommandWebhook() CommandWebhookStore
 	Preference() PreferenceStore
 	License() LicenseStore
 	Token() TokenStore
@@ -326,6 +327,13 @@ type CommandStore interface {
 	AnalyticsCommandCount(teamId string) StoreChannel
 }
 
+type CommandWebhookStore interface {
+	Save(webhook *model.CommandWebhook) StoreChannel
+	Get(id string) StoreChannel
+	TryUse(id string, limit int) StoreChannel
+	Cleanup()
+}
+
 type PreferenceStore interface {
 	Save(preferences *model.Preferences) StoreChannel
 	Get(userId string, category string, name string) StoreChannel