Retag images to reduce time spent on recomputing unchanged docker images

[corneliusroemer]

Summary

Bypass building docker images when all relevant input files have not changed (akin to NixOS)

• Calculate hash of all files relevant for docker build
• Add that hash as a tag to all built images
• For future builds, only run builds when there's no docker image with the input file dir hash

This way, docker builds are only done when necessary. You change website only in a commit, then no need to build a new backend docker image.

Docker build times were roughly:

• 1.30min for Nextclade, though sometimes only 30s if (separate from this PR) docker cache hit
• 2-4min for website
• 2-3min for backend

The bypass workflow completes in 20s.

Benefit is not just that we save a few Github action minutes, but also that preview builds are up much faster when only config is changed, this should be particularly helpful for @theosanderson

[theosanderson]

Looks cool

[chaoran-chen]

Cool! How much time is it saving and could you please provide a brief summary of what you changed? :)

[corneliusroemer]

Done @chaoran-chen

this is how fast it is now:

This was previously: