added graphviz to build packages

[peterkomar-aws]

Issue #, if available: Documentation (https://amazon-braket-pennylane-plugin-python.readthedocs.io/en/latest/code.html#class-inheritance-diagram) does not display the graph.

Description of changes: Based on this successful PR on the Pennylan repo (https://github.com/PennyLaneAI/pennylane/pull/4284), I am adding graphviz package to build environment to create.

Testing done:

I was not able to test it, because I don't have dot installed on my machine. Please help.

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[peterkomar-aws]

I run tox -e docs to build the documentation locally, but I received this warning that seemed relevant:

WARNING: dot command 'dot' cannot be run (needed for graphviz output), check the graphviz_dot setting

And the page at amazon-braket-pennylane-plugin-python/build/documentation/html/code.html still does not show the graph.

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (abe0dfe) 100.00% compared to head (a6ec788) 100.00%.

Additional details and impacted files

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  Files            7         7           
  Lines         1071      1071           
  Branches       249       249           
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  Hits          1071      1071           

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