Create Database Index for sourceChannel to Speed Up Aggregations

### Background Information

Currently, the `sourceChannel` field in the `VerificationRequest` collection is used frequently in aggregations and queries, for example when generating dashboards. Without an index, these operations can be slow on large collections because MongoDB needs to scan all documents. Adding an index would improve query performance for these operations.

### How

Create a database index on the `sourceChannel` field.
For example, in MongoDB shell:

```js
db.VerificationRequest.createIndex({ sourceChannel: 1 });
This index will allow MongoDB to quickly locate and group documents by sourceChannel, improving read performance for queries and aggregations.