Issue:
refactor(user): Make password nullable for `users`

Currently `password` is required field in `users` table. This is causing us to create temporary passwords for `users` in some APIs which inserts `users` without password.

So, we have to make password nullable to solve this.

Resolution:
<think>
PR Context:
- Title: refactor(users): Make password nullable in `users` table
- Merged: 2024-06-10T13:10:29Z
- Files changed: 7 files
- Commits: 3 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
<!-- Describe your changes in detail -->
This API will make the password column in the `users` table nullable.

### Additional Changes

- [ ] This PR modifies the API contract
- [x] This PR modifies the database schema
- [ ] This PR modifies application configuration/environmen
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** refactor(users): Make password nullable in `users` table (#4902)
Files to modify:


**crates/diesel_models/src/schema.rs**
  Modify existing code

**crates/diesel_models/src/user.rs**
  Modify existing code

**crates/router/src/core/user.rs**
  Modify existing code

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

**crates/router/src/types/domain/user.rs**
  Modify existing code