Added automated docker build process

[jasminabrar]

• added GitHub action to build docker image using Dockerfile, storing it as a package in the repo
• docker image rebuilds any time (1) a change to Dockerfile is made via a direct push or merged PR, or (2) a new version of siepic tools or ebeam pdk is released

Notes

• Currently the EBeam Tests action is referring to the docker image in my (jasminabrar) forked repo. Once this PR is merged, we can trigger the docker build action to run and the docker image will be built and pushed as a package to this main repo. Then we can change the EBeam Tests to refer to this image, and from then on will use images stored in this repo
• EBeam Tests is currently failing due to a pcell TestStruct_DoubleBus_Ring not being registered in EBeam Beta

[lukasc-ubc]

TestStruct_DoubleBus_Ring.py has been moved to the folder "broken", so all the cells should load correctly.

[lukasc-ubc]

Wow, I see the test passed! I looked in the Details and it has checked all the PCells!
Congrats on getting this working @FarihaIS and @jasminabrar!