[ACP-99] ValidatorSetManager Solidity Contract (#99)

* feat: add ACP-99

* feat: apply suggestions from code review

Co-authored-by: aaronbuchwald <[email protected]>

* feat(99): apply suggestions from code review

* feat(99): apply @aaronbuchwald suggestions

* feat(99): refresh ACP-99 to reflect implementation + ACP-77 update

* feat(99): add initializeValidatorSet function

* feat: apply @michaelkaplan13 suggestions from code review

Co-authored-by: Michael Kaplan <[email protected]>

* feat(99): refresh ACP-99 to match ACP-77

* feat(99): add an open question regarding churn control

* feat(99): update interfaces

* feat(99): update ACP99Manager interface

* feat: apply @michaelkaplan13 suggestions from code review

Co-authored-by: Michael Kaplan <[email protected]>

* feat(99): update ACP99 interfaces

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Co-authored-by: aaronbuchwald <[email protected]>
Co-authored-by: Michael Kaplan <[email protected]>