chore: Support arm/v7 and arm64 and migrate to GitHub Container Registry

[irvinlim]

This PR adds support for linux/arm/v7 and linux/arm64 architectures, releasing container images for multiple architectures using docker manifest. Additionally, we are migrating from Docker Hub to GitHub Container Registry! 🎉

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Changes

1. Follows the tutorial from GoReleaser on how to build multi-arch Docker releases: https://carlosbecker.com/posts/multi-platform-docker-images-goreleaser-gh-actions/
2. Revamp nightly release workflows and avoid using GoReleaser's snapshot feature.
3. Rewrite some ./hack scripts to use getopts.
4. Migrate from Docker Hub to GitHub Container Registry. Images can be pulled from here instead: https://github.com/orgs/furiko-io/packages

[codecov]

Codecov Report

Base: 63.50% // Head: 63.53% // Increases project coverage by +0.03% 🎉

Coverage data is based on head (6a432e6) compared to base (5ad6ccc).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
+ Coverage   63.50%   63.53%   +0.03%     
==========================================
  Files         205      205              
  Lines       10958    10957       -1     
==========================================
+ Hits         6959     6962       +3     
+ Misses       3621     3619       -2     
+ Partials      378      376       -2     

Impacted Files	Coverage Δ
pkg/utils/heap/heap.go	100.00% <0.00%> (+1.07%)	⬆️
pkg/execution/util/schedule/schedule.go	77.32% <0.00%> (+1.60%)	⬆️

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[irvinlim]

Currently on hold because this conflicts with the snapshot action.