Update JsonSerializerOptions to allow trailing commas

[Youssef1313]

This allows having trailing commas in dotnet-versionsweeper.json, so when dotnet-versionsweeper.json is updated with new entries, the diff is cleaner.

---

Before

A diff would look like:

{
    "ignore":[
-        "Entry1"
+        "Entry1",
+        "Entry2"
    ]
}

---

After

A diff would look like:

{
    "ignore":[
        "Entry1",
+       "Entry2",
    ]
}

[IEvangelist]

Looks good to me, we'll - thank you 🙏