Add default `Content-Type` header in `Disk.createHttpResponse` responses

[LoicPoullain]

Issue

When downloading a file, some navigators (might) need to always have the Content-Type header defined.

Solution and steps

• Add application/octet-stream as default Content-Type header.

Checklist

• [x] Add/update/check docs (code comments and docs/ folder).
• [x] Add/update/check tests.
• [x] Update/check the cli generators.