feat: add support for DockerfileInline

[tushar5526]

Fixes #4108

As nerdctl currently uses "nerdctl build" to build the service images, write the inline file to a temporary file and use "-f" to specify the temporary dockerfile.

TODO: Add tests if the approach looks fine.

[tushar5526]

I was a bit confused about where to place this logic: writing the inline file to a temporary path and then modifying the build command to build using that file.

It seems like Build object on Service is something that is meant to be reusable, so I placed the logic of temporary file generation at the time of parsing the service and generating the Build config.

[tushar5526]

@apostasie, can I get a cursory review of the approach?

[apostasie]

Hey @tushar5526
Looks fine to me.

You do need to make sure that dockerfile and dockerfileinline cannot be specified together though:
https://docs.docker.com/reference/compose-file/build/

[tushar5526]

It looks like composecli package "github.com/compose-spec/compose-go/v2/cli" is already doing that job for me.

[AkihiroSuda]

Please squash and sign off the commits.
(make sure that the Signed-off-by: NAME <EMAIL> line with your real name is included in the commit message)

[tushar5526]

Done, thanks!

[AkihiroSuda]

CI is failing
https://github.com/containerd/nerdctl/actions/runs/15929816575/job/44936014200?pr=4305

FAIL - has whitespace errors. See git show --check 5651e76d85e12092b65f3e35b8994d2244e35698.