docs: added a ramification of opt out

[insumity]

Description

Added a ramification of ADR 009, namely that soft opt-out would delay the decision of blocks on consumer chains.

Probably, the most relevant document to read about rounds on the underlying Tendermint consensus algorithm is The latest gossip on BFT consensus paper where, among others, it's written:

The algorithm proceeds in rounds, where each round has a dedicated proposer. The mapping of rounds to proposers is known to all processes and is given as a function proposer(h, round), returning the proposer for the round round in the consensus instance h.

And then in the pseudocode presented in Algorithm 1, we can see that if a proposer is down, other validators would prevote on nil and eventually OnTimeoutPrecommit would be called and increase the round number.

Thanks to @sergio-mena for mentioning this!

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[insumity]

Tiny change because PR was failing on markdown-link checking.
We could also use Nitter instead but it's quite likely for Nitter to be down once in a while.

[p-offtermatt]

Is it easy to add a reference to the code that shows that this is happening?
I think it's probably hard, but if possible it would be cool to have something here
that future readers can check to convince themselves this is the behaviour

[mpoke]

Nice catch

[insumity]

@p-offtermatt

Is it easy to add a reference to the code that shows that this is happening?
I think it's probably hard, but if possible it would be cool to have something here
that future readers can check to convince themselves this is the behaviour

I think it might be a bit confusing to point to CometBFT code snippets as part of this ADR. It could be done though if you think it would add value.
I augmented the description in the PR with a pointer to the Tendermint paper. I feel that would be a more reasonable starting point for someone that would be interested in this. Again, I felt it might be a bit too much to add this information on the actual ADR.

[p-offtermatt]

Yup, that works for me, thanks for going through the trouble!