Fix: Backend now binds parametric circuits before execution

[ameyer-rigetti]

NOTE: Merging into omit-barriers to release both together

Behavior implemented according to execute() docs:

parameter_binds (list[dict]): List of Parameter bindings over which the set of
    experiments will be executed. Each list element (bind) should be of the form
    ``{Parameter1: value1, Parameter2: value2, ...}``. All binds will be
    executed across all experiments, e.g. if parameter_binds is a
    length-n list, and there are m experiments, a total of :math:`m x n`
    experiments will be run (one for each experiment/bind pair).

[dbanty]

Not sure about the Qiskit specifics but the Python looks good. Made a couple optional suggestions