Proposer selection upgrade and proposer set voting protocol in fallback case

[drewstone]

Summary of changes Changes introduced in this pull request:

• [x] In an effort to simplify operations of the bridge and handle the propser set voting protocol seamlessly, we make the restriction that proposers can only be active validators.
• [ ] We use the proposers to watch the chain in the event we force_change_authorities.
• [ ] If the force_change_authorities extrinsic is called, we have the proposers sign the Vote with their ECDSA keys and gossip similarly to how we gossip misbehaviours
• [ ] We store these votes for any relayer to grab and apply.

Reference issue to close (if applicable)

Closes

[codecov-commenter]

Codecov Report

Patch coverage: 43.30% and project coverage change: -2.24 :warning:

Comparison is base (efb068b) 19.28% compared to head (e28294a) 17.04%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #633 +/- ## ========================================== - Coverage 19.28% 17.04% -2.24% ========================================== Files 75 77 +2 Lines 4981 5548 +567 ========================================== - Hits 960 945 -15 - Misses 4021 4603 +582 ``` | [Impacted Files](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools) | Coverage Δ | | |---|---|---| | [pallets/dkg-proposals/src/benchmarking.rs](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools#diff-cGFsbGV0cy9ka2ctcHJvcG9zYWxzL3NyYy9iZW5jaG1hcmtpbmcucnM=) | `0.00% <ø> (ø)` | | | [pallets/dkg-proposals/src/weights.rs](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools#diff-cGFsbGV0cy9ka2ctcHJvcG9zYWxzL3NyYy93ZWlnaHRzLnJz) | `0.00% <ø> (ø)` | | | [pallets/dkg-metadata/src/lib.rs](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools#diff-cGFsbGV0cy9ka2ctbWV0YWRhdGEvc3JjL2xpYi5ycw==) | `23.26% <6.90%> (-0.75%)` | :arrow_down: | | [dkg-runtime-primitives/src/traits.rs](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools#diff-ZGtnLXJ1bnRpbWUtcHJpbWl0aXZlcy9zcmMvdHJhaXRzLnJz) | `14.29% <20.00%> (-19.04%)` | :arrow_down: | | [pallets/dkg-proposals/src/lib.rs](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools#diff-cGFsbGV0cy9ka2ctcHJvcG9zYWxzL3NyYy9saWIucnM=) | `73.52% <60.66%> (-4.97%)` | :arrow_down: | | [dkg-runtime-primitives/src/lib.rs](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools#diff-ZGtnLXJ1bnRpbWUtcHJpbWl0aXZlcy9zcmMvbGliLnJz) | `36.00% <100.00%> (ø)` | | ... and [27 files with indirect coverage changes](https://app.codecov.io/gh/webb-tools/dkg-substrate/pull/633/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webb-tools)

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