Support rootless Docker to build firmware

[DBLouis]

The problem you're addressing (if any)

It would be nice to be able to build the firmware with a rootless Docker install.

Describe the solution you'd like

Maybe having a second Docker image and a optional parameter to the build.sh script is good enough.

Where is the value to a user, and who might that user be?

No response

Describe alternatives you've considered

In the meantime, I was able to make it work by simply rebuilding the coreboot-sdk image like this:

FROM coreboot/coreboot-sdk:version
USER root

And modifying build.sh accordingly, replacing the image name and removing -u $UID for each docker command.

Additional context

No response