v7: Add image for intel oneAPI (SYCL) (#26)

This uses the same Ubuntu 20.04 image we use anyway. I'm installing Intel's stuff from their APT repo. This only clocks in at ~ 3GB, rather than the 6GB of the Intel image. I managed to compile the SYCL plugin with this.

v6

Switch LCG images to LCG 97/98 and archive obsolete images.

v5

Move images to the Github container registry.

v4

Add image based on Ubuntu 18.04 that has CUDA compiler (#21)

v3

Fix gcc setup in LCG images (#20)

v2

Fix LCG images (#19)

v1

update CentOS 7 images (#17)