feat: add reply functionality to thoughts, including database migration and tests

thoughts-backend/models/src/params/thought.rs

@@ -1,5 +1,6 @@
 use serde::Deserialize;
 use utoipa::ToSchema;
+use uuid::Uuid;
 use validator::Validate;
 
 #[derive(Deserialize, Validate, ToSchema)]
@@ -10,4 +11,6 @@ pub struct CreateThoughtParams {
         message = "Content must be between 1 and 128 characters"
     ))]
     pub content: String,
+
+    pub reply_to_id: Option<Uuid>,
 }