Initial Halo2 Plugin

[bhgomes]

Signed-off-by: Brandon H. Gomes bhgomes@pm.me

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Before we can merge this PR, please make sure that all the following items have been checked off:

• Linked to an issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Added one line describing your change in CHANGELOG.md and added the appropriate L- label to the PR.
• Re-reviewed Files changed in the GitHub PR explorer.
• Checked that changes and commits conform to the standards outlined in CONTRIBUTING.md.