feat: added new commands

- added follow command
- added unfollow command
- following command
- introduced logged in user middleware

sql/schema/003_follows.sql

@@ -0,0 +1,14 @@
+-- +goose Up
+CREATE TABLE follows (
+  id UUID PRIMARY KEY,
+  created_at TIMESTAMP NOT NULL,
+  updated_at TIMESTAMP NOT NULL,
+  user_id UUID NOT NULL,
+  feed_id UUID NOT NULL,
+  FOREIGN KEY(user_id) REFERENCES users(id) ON DELETE CASCADE,
+  FOREIGN KEY(feed_id) REFERENCES feeds(id) ON DELETE CASCADE,
+  CONSTRAINT unique_user_feed UNIQUE(user_id, feed_id)
+);
+
+-- +goose Down
+DROP TABLE follows;