Incremental cache in Docker cluster

[AhmedMozaly]

Although I've just created a PoC PR, but better to have the discussion here:

When building a docker image, There are two types of cache content that Docker maintain between builds:

• Image layer caching (to help reduce the amount of layer downloaded from registry)
• Mount/Incremental cache (to keep the files generated between builds, like /root/.npm)

Both cache content are served/handled by the local Docker daemon, this means that an image built on specific Docker host. need to be built on the same host each time to take full advantage of caching capabilities

This PR enables Nixpacks to work more smoothly in a cluster setup (Multiple Docker nodes accessing cache remotely)
After build command runs (for example npm run build) the directories need to be cached (like /root/.npm) will be archived with tar and sent to a small HTTP server that has been started by Nixpacks to receive these files

These tar files -if available- will be copied back to any newer image build. It will extracted to the right location inside the image to help build tools find out the files needed for the build without the needed to re-download it.

Plan:

• Start small HTTP server before building the image
• Send directories need to be cached to the HTTP server
• Copy back the cached directories -if exists- to the image before running the build command
• Handle port assignment for the HTTP server
• Package the cached directories into OCI image & push to an image registry

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Feedback is welcomed!