chore: #3604079 Change the logo and emblem to the new approved Varbase brand logo for Varbase Project

Adds the new approved Varbase brand emblem to the Varbase Project template and updates the README logo.

• Adds logo.png (new emblem).
• Updates the README logo image to the Varbase profile varbase-logo.png served from GitHub (https://raw.githubusercontent.com/Vardot/varbase/11.0.x/images/varbase-logo.png).
• Adds the standard Varbase .gitlab issue and merge request templates.

Depends on https://www.drupal.org/project/varbase/issues/3603617 (adds images/varbase-logo.png to the Varbase profile).

Issue: https://www.drupal.org/project/varbase_project/issues/3604079

AI-Generated: Yes (Used Claude Code to add the new approved Varbase emblem and update the README logo image).

Checkpoints

• File an issue about this project
• Addition/Change/Update/Fix to this project
• Testing to ensure no regression
• Automated unit/functional testing coverage
• Developer Documentation support on feature change/addition
• User Guide Documentation support on feature change/addition
• UX/UI designer responsibilities
• Accessibility and Readability
• Code review from 1 Varbase core team member
• Full testing and approval
• Credit contributors
• Review with the product owner
• Update Release Notes
• Release