Composite Operator: feature for composing quantum operations at a high level

[jrrhuang]

Issue #, if available: NA

Description of changes: This feature supports building decomposable quantum operations for high level quantum algorithms. Moreover, it allows quantum circuits to be compartmentalized into distinct sub operations when visualizing.

Testing done:

• ./test/unit_tests/braket/circuits/test_composite_operator.py: tested composite_operator base class; covered all class methods and constructor __init__
• ./test/unit_tests/braket/circuits/test_composite_operators.py: tested composite operators for GHZ, QFT, and QPE; covered all class methods and decompositions using one instance each (maybe can add more instances with different qubit inputs in the future)
• ./test/unit_tests/braket/circuits/test_ascii_circuit_diagram.py: tested composite operator ascii circuit diagram
• ./test/unit_tests/braket/circuits/test_circuits.py: tested decompose function on circuit object
• ./test/unit_tests/braket/circuits/test_instruction.py: tested decompose function on instruction object

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