Issue:
refactor: alter query for merchant scoped metadata

Remove `is_null` from `find_merchant_scoped_dashboard_metadata`
This is done to make DB changes and support backward compatibility in next deployment.

Resolution:
<think>
PR Context:
- Title: refactor(dashboard_metadata): alter query for merchant scoped metadata
- Merged: 2024-07-22T13:56:29Z
- Files changed: 2 files
- Commits: 1 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
Alter query in `find_merchant_scoped_dashboard_metadata`
For merchant scoped metadata it need not to be considered whether user_id column is `null` or not


### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** refactor(dashboard_metadata): alter query for merchant scoped metadata (#5397)
Files to modify:


**crates/diesel_models/src/query/dashboard_metadata.rs**
  Modify existing code

**crates/router/src/db/dashboard_metadata.rs**
  Modify existing code