Simplify and shift to Awesome List + Minimal Gateway

[anjackson]

Following these discussions: https://github.com/orgs/digipres/discussions/34

For digipres.org:

• [x] Simplify the digipres.org homepage, using the banners to link to the relevant sections of the Awesome List, or the COPTR Tools grid, Q&A, corpora, etc, as appropriate.
• [x] Drop the Contributions section.
• [x] Link to https://github.com/orgs/digipres/discussions for general discussions about these resources.

For the Awesome List, see digipres/awesome-digital-preservation#1

[anjackson]

After some forcible re-writing of history, I've managed to link the history of the index.md to the README.md, although its surprisingly clunky: https://github.com/digipres/awesome-digital-preservation/commits/64ab11db7e9efa2e3b2634e595455c6f19f912e4/index.md?browsing_rename_history=true&new_path=README.md&original_branch=main

[anjackson]

I've separated out the Awesome List work into it's own ticket: digipres/awesome-digital-preservation#1

Will probably also break some items out into their own tickets and defer them as I can't get everything done in time for WDPD.

[anjackson]

Deferring #39 #40