[IMP] web: sample data in reporting views (preparatory work)

The present commit brings the global changes necessary to have sample
data in the reporting views. This includes several modifications/
fixes of the sample server (many of them for better visual results).

Task ID: 2282196

Co-authored-by: Aaron Bohy <aab@odoo.com>
Co-authored-by: Mathieu Duckerts-Antoine <dam@odoo.com>