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.

internal/db/services/welcome/service.go

@@ -0,0 +1,36 @@
+package welcome
+
+import (
+	"context"
+
+	"velox-bot/internal/db/repos/welcomerepo"
+)
+
+type Service struct {
+	repo *welcomerepo.Repo
+}
+
+func New(repo *welcomerepo.Repo) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) GetSettings(ctx context.Context, guildID int64) (*welcomerepo.Settings, error) {
+	return s.repo.GetSettings(ctx, guildID)
+}
+
+func (s *Service) SetChannel(ctx context.Context, guildID, channelID int64) error {
+	return s.repo.UpsertChannel(ctx, guildID, channelID)
+}
+
+func (s *Service) SetMessage(ctx context.Context, guildID int64, message string) error {
+	return s.repo.UpsertMessage(ctx, guildID, message)
+}
+
+func (s *Service) SetDM(ctx context.Context, guildID int64, dm string) error {
+	return s.repo.UpsertDM(ctx, guildID, dm)
+}
+
+func (s *Service) SetGIF(ctx context.Context, guildID int64, gifURL string) error {
+	return s.repo.UpsertGIF(ctx, guildID, gifURL)
+}
+