fix: missing swap event for cw pool (backport #7938)

[mergify]

Closes: #XXX

What is the purpose of the change

Numia team has a problem tracking swap events for a CW pool. The reason is that the event is missing.

Context: https://osmosis-network.slack.com/archives/C04M8FQ5Y2G/p1712020788660349

While there is a workaround that they can implement, it would be a hack looking for events at another layer of abstraction.

I propose adding this change to the v24 scope. The core of the change is emitting the swap event in x/cosmwasmpool.

I evaluated the option of emitting this at the poolmanager layer. However, given that we have many swap APIs, it would take some careful effort to make sure that nothing is missed. Given the above, it is cleaner and less risky to simply add the event at the x/cosmwasmpool level.

Given that events are now state breaking, it is important to account for the above risks.

Documentation and Release Note

• Does this pull request introduce a new feature or user-facing behavior changes?
• Changelog entry added to Unreleased section of CHANGELOG.md?

Where is the change documented?

• Specification (x/{module}/README.md)
• Osmosis documentation site
• Code comments?
• N/A

Summary by CodeRabbit

• New Features
  • Introduced missing swap events for CW pools to enhance transparency and tracking of swap activities.
• Refactor
  • Revised swap event emission logic to occur at the pool module layer, improving modularity and clarity in event handling across different pool modules.
• Documentation
  • Added comments to clarify the new approach for emitting swap events, ensuring better understanding and implementation in future developments.

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This is an automatic backport of pull request #7938 done by [Mergify](https://mergify.com).