Replace GCBM container with moja.canada package

[aornugent]

#63 included an updated Docker build for the GCBM container and #65 + #70 published them on the Github Container Repository.

However, #29 also publishes an image for the GCBM. The build in the FLINT.cloud repository can be simplified to draw from the correct source.

It's slightly circular that moja.canada pulls from FLINT.cloud then FLINT.cloud pulls from moja.canada, but this is necessary until #116 is merged upstream.