Build OCI-compatible image cache

[angonz]

Fixes #1118

Add image-manifest=true to build context to support OCI-compatible image cache.
This allows using the registry cache in other registries, like AWS ECR.

[regisb]

🤔 According to my tests this change should not break our CI. But I'm not sure what's the impact, to be honest. I fail to understand this part of the docs: https://docs.docker.com/build/cache/backends/

By default, the OCI media type generates an image index for the cache image. Some OCI registries, such as Amazon ECR, don't support the image index media type: application/vnd.oci.image.index.v1+json. If you export cache images to ECR, or any other registry that doesn't support image indices, set the image-manifest parameter to true to generate a single image manifest instead of an image index for the cache image.

I am tempted not to merge this change, for the following reasons:

1. I don't really have a clue what this does.
2. It makes the build command more complicated.
3. You can achieve the same result by implementing the DOCKER_BUILD_COMMAND filter https://docs.tutor.edly.io/reference/api/hooks/catalog.html#tutor.hooks.Filters.DOCKER_BUILD_COMMAND

[angonz]

Hi Régis!
To be honest, I stopped using the registry cache because it only slows the image building process. Registry cache seems to be tied to the image tag. As we create a new tag for every build, cache is always regenerated. Btw, I didn't know of the DOCKER_BUILD_COMMAND setting. That might be a better alternative.

[DawoudSheraz]

Given the conversations above, are we good to close this PR @angonz?

[angonz]

Yes.