Update to latest astro version, clean up tech debt
Updates astro (2.2.0 -> 4.16.10). https://docs.astro.build/en/guides/upgrade-to/v3/ & https://docs.astro.build/en/guides/upgrade-to/v4/
Removes astro-imagetools. Astro >=v3 has its own image optimiser, implements that.
Update version of node for CI/CD as astro v4 does not support node 16.
Cleans up some references to non-existent classes originating from the orginal tailwindcss version of the homepage, which now don't exist.
Classes include:
- p-3
- py-3
- pt-5
- my-3
- ml-7
- mb-3
- mb-9
- list-disc
- bg-blue-100
- bg-amber-100
- md:grid-cols-2
- text-xl
- text-3xl
- font-bold
- text-center
No visual changes to site