Attestable Switch class

[niksu]

This PR adds the Attestable Switch class and related functionality.
A FABRIC Artifact will be added to demonstrate how to use this functionality.
The code added in this PR is derived from beta 2 of the CREASE prototype (http://crease.cs.iit.edu/) which has been stable for the last few weeks, which gives us confidence that it's safe to upstream to fablib.
Through this class FABRIC users, will have the option to use attestable switch features, but can also use this as a convenient wrapper for BMv2.

[kthare10]

@niksu - Tests are passing in the workflow. So, I think that's okay.
However, could you please address the two failures noted in Git workflow?

• Add documentation to the code in attestable_switch.py
• Add an entry to ChangeLog.md about the changes made.

[github-actions]

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[kthare10]

Looks good!