fix: Allow passing css var to change Collabora logo color

[elzody]

• Target version: main

Summary

Allows a user to set custom css values for the logo background color and logo visibility in Collabora.

Example:

:root {
  /* change the background color of the logo */
  --nc-logo-background: cyan;

  /* or hide the logo completely */
  --nc-logo-display: none;
}

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Documentation (manuals or wiki) has been updated or is not required