Remove arm64 build

[danielhollas]

Closes #775

• Removed arm64 build to reduce complexity
• moved Dockerfile to the root directory and removed build.json and docker-build.hcl. Image can now be build by docker build . -t aiidalab/qe:newbuild
• Only push image to ghcr.io, not to dockerhub. I think this is sufficient for this image.
• Removed the Firefox tests, both for CI speed and simplicity. As long as we've been running these UI tests in AWB and my app, we've never caught any bug that would be specific for Firefox. Given Firefoxe's low usage, I think we can skip it here and only test with Chrome. Since these tests do not run in parallel this saves a fair amount of time (>2min). And it also makes the workflow simpler. We'll still continue testing Firefox in AWB to make sure individual widgets work there.

[danielhollas]

@unkcpz @superstar54 I need to re-enable the integration tests but otherwise this is good for initial review. Let's get this PR merged before the other.

(-400 lines of YAML and configuration!)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.28%. Comparing base (4d7cadc) to head (6417c11).
Report is 44 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #776   +/-   ##
=======================================
  Coverage   68.28%   68.28%           
=======================================
  Files          45       45           
  Lines        4143     4143           
=======================================
  Hits         2829     2829           
  Misses       1314     1314           

Flag	Coverage Δ
python-3.10	68.28% <ø> (ø)
python-3.9	68.31% <ø> (ø)

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[danielhollas]

Tests are back and passing.

[unkcpz]

Thanks! @danielhollas Just one minor request, then good to go.

[unkcpz]

Approved, thanks! Let's wait tests.