Add Pimcore Expert chatmode (#415)

- Expert assistant for Pimcore CMS, DAM, PIM, and E-Commerce
- Covers DataObjects, Symfony integration, and E-Commerce Framework
- Includes comprehensive code examples and best practices

Co-authored-by: Lyubomir Filipov <[email protected]>
Co-authored-by: Aaron Powell <[email protected]>

Author: 3 people