feat: add welcome message functionality

- Introduced a new welcome service and repository for managing welcome messages, channels, and GIFs.
- Added commands to set welcome channel, message, DM, and GIF through the bot's configuration.
- Implemented event handling for new guild members to send welcome messages and DMs based on configuration.
- Updated main application to include the new welcome service in the bot's services.

schema.sql

@@ -19,8 +19,6 @@ CREATE TABLE IF NOT EXISTS twitch (
 CREATE TABLE IF NOT EXISTS levelsettings (
     guild_id BIGINT PRIMARY KEY,
     levelsys BOOLEAN NOT NULL DEFAULT FALSE,
-    role BIGINT,
-    levelreq INT,
     message TEXT
 );