Design documentation content needs update

[MuhtasimTanmoy]

Describe the change

While going through the documentation, found the following content links invalid.

From docs/crates/db.md

• File: crates/stages/src/db.rs
• File: crates/storage/provider/src/transaction.rs

From docs/design/metrics.md

• Stages metrics describer

Also, should the reference code snippet below be updated?

Additional context

No response

[github-actions[bot]]

This issue is stale because it has been open for 21 days with no activity.