chore: changelog & upgrading documentation for ABCI++

[tac0turtle]

Description

Closes: #12272

this adds a changelog for changes from integrating comet 0.38

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[julienrbrt]

Slightly unrelated but posting this here, so we can add it in the changelog as well: #16043 (comment) (and then I can close a tab)

[julienrbrt]

two nits (the link and the title). We will still need docs for updating the flow.
We still require docs to update the baseapp core concepts and describe finalize block, verify vote extensions, etc..
It will be great as well to add a disclaimer here: https://docs.cosmos.network/v0.50/building-modules/beginblock-endblock about what means BeginBlock and EndBlock now.

[julienrbrt]

ACK. I guess the other updates I suggested could be done in another issue as part of QA: #16315 (review)

[tac0turtle]

ACK. I guess the other updates I suggested could be done in another issue as part of QA: #16315 (review)

#16481

i will pick this up