[FIX] base,l10n_ch: Display all QR codes in QR bill

Issue:

  When trying to print a Suisse QR bill, if multiple images are presents
  in document and they have a url as src, some pictures will not be
  displayed.
  (Same issue may occur with simple QR code)

Cause:

  It's a known issue with wkhtmltopdf: https://github.com/odoo/odoo/commit/2949138a7d84cd6c925ea1745d62f25ef077bb8b


  Also, adding css class to body by js break wkhtmltopdf.

Solution:

  Replace link by base64 image value (use a function to retrieve base64
  image instead of image_url).
  Remove class 'l10n_ch_qr' added by js (no need since CSS file didacted
  to this report).

  extra: Alter some css for better rendering.

opw-2620082

closes odoo/odoo#75408

Signed-off-by: oco-odoo <oco-odoo@users.noreply.github.com>