Upgrade/dockerfile v0.33

[vincentmr]

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---

Context:
L-GPU can now be built from the pennylane-lightning repo. The Dockerfile can be updated accordingly.

Description of the Change:
Update README and L-GPU build stage.

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (23f9d92) 96.96% compared to head (191ffc3) 96.96%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #539    +/-   ##
========================================
  Coverage   96.96%   96.96%            
========================================
  Files         144      145     +1     
  Lines       17183    17323   +140     
========================================
+ Hits        16661    16798   +137     
- Misses        522      525     +3     

Files	Coverage Δ
pennylane_lightning/core/_version.py	100.00% <100.00%> (ø)

... and 13 files with indirect coverage changes

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[AmintorDusko]

Nice work! I left some suggestions.