Usa a stable Zola release

[senekor]

We are currently using a fork, because we rely on a few patches on top of Zola. Ideally these (or an alternative that suits us) can be upstreamed. This issue is to keep track of the upstreaming progress.

The version of zola we install is a specific commit hash. That commit merges all patches we rely on and has a summary of them all as its commit message: senekor/zola@620bf3c

🚧 Unmerged:

• Enable rendering our releases.json feed
  • currently used patch: senekor/zola@f813dee
  • pending PR: Allow json and ics templates for custom feeds getzola/zola#2856

⏳️ Merged, but not yet released:

• Alias: preserve the hash when redirecting
  • currently used patch: senekor/zola@2e63e41
  • merged PR: Alias: preserve the hash when redirecting getzola/zola#2851
• Allow generating empty feeds (applies to our inside-rust/releases.json)
  • currently used patch: senekor/zola@f4c69f8
  • merged PR: Allow generating empty feeds getzola/zola#2850
• Allow us to sort pages by their permalink (which is effectively sorting by date, because the permalink of each post starts with its date of publication)
  • currently used patch: senekor/zola@fe820e3
  • pending PR: Add permalink sorting getzola/zola#2857