chore: increase custom theme limit

Author: Miodec

backend/__tests__/dal/user.spec.ts

@@ -1729,7 +1729,7 @@ describe("UserDal", () => {
     it("should return error if user has reached maximum", async () => {
       // given
       const { uid } = await UserTestData.createUser({
-        customThemes: new Array(10).fill(0).map(() => ({
+        customThemes: new Array(20).fill(0).map(() => ({
           _id: new ObjectId(),
           name: "any",
           colors: [] as any,

backend/src/dal/user.ts

@@ -685,7 +685,7 @@ export async function addTheme(
   const _id = new ObjectId();
 
   await updateUser(
-    { uid, "customThemes.9": { $exists: false } },
+    { uid, "customThemes.19": { $exists: false } },
     {
       $push: {
         customThemes: {