This adds support to loading artifacts (e.g. docker.#Build,
os.#Container, ...) into any arbitrary docker engine (through a
dagger.#Stream for UNIX sockets or SSH for a remote engine)
Implementation:
- Add op.#SaveImage which serializes an artifact into an arbitrary path
(docker tarball format)
- Add docker.#Load which uses op.#SaveImage to serialize to disk and
executes `docker load` to load it back
Caveats: Because we're doing this in userspace rather than letting
dagger itself load the image, the performance is pretty bad.
The buildkit API is meant for streaming (get a stream of a docker image
pipe it into docker load). Because of userspace, we have to load the
entire docker image into memory, then serialize it in a single WriteFile
LLB operation.
Example:
```cue
package main
import (
"alpha.dagger.io/dagger"
"alpha.dagger.io/docker"
)
source: dagger.#Input & dagger.#Artifact
dockersocket: dagger.#Input & dagger.#Stream
build: docker.#Build & {
"source": source
}
load: docker.#Load & {
source: build
tag: "testimage"
socket: dockersocket
}
```
Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>
