add competition service (it`s broken, I will fix it later)

internal/competition/domain/errors.go

@@ -0,0 +1,8 @@
+package domain
+
+import "errors"
+
+var (
+	ErrCompetitionNotFound      = errors.New("competition not found")
+	ErrInvalidCompetitionData   = errors.New("invalid competition data")
+)