Added article on advanced MoveIt manipulator planning (fall) and Gazebo simulator (spring)

[tomputer-g]

Hello,
This is zimingg@ from MRSD Team E requesting review and addition of my article.

Thank you.

[nevalsar]

Added fixes to align with project standards:

• Adjusted heading levels to start from H2 for proper hierarchy.
• Converted HTML image tags to standard Markdown with absolute paths and descriptive alt text.
• Moved images to the central repository (/assets/images/adv-moveit-manipulator-planning/).
• Formatted raw URLs in the Gazebo article into descriptive Markdown links for better readability.
• Added entries for both articles to their respective category index pages for better discoverability.
• Fixed minor formatting issues (missing newlines).