Adjust imports in aqc plugin to avoid discovery overhead (#7327)
Adjust imports in aqc plugin to avoid discovery overhead (#7327)

This commit tweaks the imports for the aqc plugin to make the optimizer
and other aqc method imports occur at run time only. Previously these
were done at the module level, which is normally best practice for many
reasons, but in this specific case doing plugin discovery causes the
module to be loaded (and the plugin class instaniated) even if the
plugin is not specified by the user. The imports for aqc are fairly
heavy as both the algorithms tree and scipy can be slow to load. To
avoid the overhead on discovery these imports are moved to runtime so we
only load them if the aqc plugin is used and these imports are needed.

Co-authored-by: Jake Lishman <4506a86e64ee7f74713ab69aff49c78428b27754@ibm.com>
QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py