Re-link social media icons on start page header banner and in footer

• Link SDV X, LinkedIn, Instagram and YouTube channels in lieu of the Eclipse Foundation ones (s. below)
• Remove Facebook icon
• Add Instagram icon

X: https://x.com/SDVeclipse

LinkedIn: https://www.linkedin.com/showcase/software-defined-vehicle/

YouTube: https://www.youtube.com/@EclipseSDV

Instagram: www.instagram.com/eclipsesdv/

Adding @paulinagueorguieva @sgallian for review

Also @sgiacomoni2as FYI as requested. Feel free to edit/change.