Emit header in MsgUpdateClient events (bp #8624)

[mergify]

This is an automatic backport of pull request #8624 done by Mergify.

Cherry-pick of a9b034b has failed:

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Your branch is up to date with 'origin/release/v0.41.x'.

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Changes to be committed:
	modified:   x/ibc/core/02-client/keeper/client.go
	modified:   x/ibc/core/02-client/keeper/client_test.go
	modified:   x/ibc/core/02-client/types/encoding.go
	new file:   x/ibc/core/02-client/types/encoding_test.go
	modified:   x/ibc/core/02-client/types/events.go
	modified:   x/ibc/core/spec/06_events.md

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

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[codecov]

Codecov Report

Merging #8770 (2500474) into release/v0.41.x (3aaf1bc) will increase coverage by 0.00%.
The diff coverage is 84.61%.

@@               Coverage Diff                @@
##           release/v0.41.x    #8770   +/-   ##
================================================
  Coverage            61.95%   61.96%           
================================================
  Files                  612      612           
  Lines                35417    35430   +13     
================================================
+ Hits                 21942    21953   +11     
- Misses               11155    11156    +1     
- Partials              2320     2321    +1     

Impacted Files	Coverage Δ
x/ibc/core/02-client/types/encoding.go	60.00% <77.77%> (+6.15%)	⬆️
x/ibc/core/02-client/keeper/client.go	98.27% <100.00%> (+0.06%)	⬆️

[alessio]

This has been reverted due to concerns that it could be state machine breaking

[colin-axner]

This has been reverted due to concerns that it could be state machine breaking

What are the concerns?

[aaronc]

AFAIK events are part of consensus and this is thus state machine breaking. @marbar3778 would know for sure from the TM side

[colin-axner]

We will test the merged commit again against the hub and/or figure out why there was no consensus failure during the first test.

[colin-axner]

This has been reverted due to concerns that it could be state machine breaking

see comment

[alessio]

@zmanian @marbar3778 @shahankhatch can we make a decision on this, please?

[tac0turtle]

Its fine to merge IMO. If it helps why not.

[zmanian]

I think Events are not hashed into gaia on the Hub right but I am only 70% confident this is the case.

Some investigation would be good. @marbar3778 are you confident?

[tac0turtle]

It is safe to merge this, in the spec https://docs.tendermint.com/master/spec/core/data_structures.html#header we mention not hashing the events. I missed it earlier. Colin did a deep dive in the code as well, we confirmed it is not.

[alessio]

Commit has been reintroduced. This is back in v0.42.0 milestone