Add matrix representation of gates to docstrings

[kshitijc]

What did you find confusing? Please describe.
The documentation for the supported gates don't sufficiently describe the action of these gates or how each of the parameters are used.

Describe how documentation can be improved
The docstring for each gate implemented here should show the matrix representation of the gate.

Additional context

[AbeCoull]

As a point of discussion for the issue, it would seem to make sense to have the docstrings using the math directive so the matrices render correctly in the docs.

[speller26]

For reference, look at how gate matrices are written in the PennyLane plugin

[rmshaffer]

Related: Each gate currently has documentation generated in three separate places, none of which are particularly useful in terms of telling what the gate or its parameters do. For example, CPhaseShift is documented in these three places:

1. https://amazon-braket-sdk-python.readthedocs.io/en/stable/_apidoc/braket.circuits.gate.html#braket.circuits.gate.Gate.CPhaseShift
2. https://amazon-braket-sdk-python.readthedocs.io/en/stable/_apidoc/braket.circuits.gates.html#braket.circuits.gates.CPhaseShift
3. https://amazon-braket-sdk-python.readthedocs.io/en/stable/_apidoc/braket.circuits.circuit.html#braket.circuits.circuit.Circuit.cphaseshift

Arguably the 3rd one is what users would look up first (if they are calling the gate methods via the Circuit class), and this is likely the least helpful one.

Maybe this should be a separate issue (I'm happy to create a new issue if desired, just let me know) but I wanted to mention it.

[ykharkov]

Closing the issue, since the PR addressing the issue was merged: #756