feat(x/gov): emit proposer address in submit proposal event (backport #19842)

[mergify]

Description

Closes: #19831

Emit proposer address with submit_proposal event.

• Key: proposal_proposer
• Value: proposer address

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Author Checklist

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please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• confirmed ! in 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
• reviewed "Files changed" and left comments if necessary
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• updated the relevant documentation or specification, including comments for documenting Go code
• 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 all author checklist items have been addressed
• reviewed state machine logic, API design and naming, documentation is accurate, tests and test coverage

Summary by CodeRabbit

• New Features
  • Enhanced proposal submission by including the proposer's information in event emissions. This allows for better tracking and visibility of proposal initiators.

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This is an automatic backport of pull request #19842 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 4599439 has failed:

On branch mergify/bp/release/v0.50.x/pr-19842
Your branch is up to date with 'origin/release/v0.50.x'.

You are currently cherry-picking commit 45994391a.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   x/gov/keeper/proposal.go
	both modified:   x/gov/types/events.go

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[julienrbrt]

Todo: fix conflicts and add changelog