Add heading anchor icons for linkable sections

[mandrasch]

Would be cool for longer posts like https://ddev.com/blog/setting-up-a-go-development-environment/ or https://ddev.com/blog/working-with-vite-in-ddev/ where reader wants to link to a specific section

Astro already assigns ids for h2,h3, etc.

Found solutions like this, first quick search:

• https://www.itaydafna.dev/blog/my-take-on-astro-markdown-anchor-headings/
• https://jan-mueller.at/blog/next-level-heading-anchors/
• https://caseyjamesperno.com/blog/astro-header-anchors/

Happy to help if this is interesting

[rfay]

Please do, thanks!