Add function to get available QEM techniques

[jordandsullivan]

Issue Description

Currently there does not appear to be a way to easily retrieve all the possible QEM techniques which are available in Mitiq.

Proposed Solution

Two potential solutions come to mind:

1. Add this information in the mitiq.about() method. This is where information like current versions of various integrations are listed (e.g. amazon braket, cirq)

2. [My preferred solution] Create a new function in mitiq/utils and add it to the mitiq/init.py called something like mitiq.qem_methods().

Additional References

NA

[github-actions]

Hello @jordandsullivan, thank you for your interest in Mitiq!
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[cosenal]

Out of curiosity, what would be a programmatic use case of this function? In other words, why isn't a wiki/documentation enough?

[nathanshammah]

@jordandsullivan I like your proposal, and the about is more for grep/OS informations. @cosenal as a Mitiq user for me it would come handy also to remind myself of module naming. Currently the wiki is a more static location mostly for roadmapping, or for researchers to understand areas of planned development; I see this as a useful tool for a lazy coder (like me). @jordandsullivan do you want to assign yourself to this issue? I'd say go for it!