Send protocol fees from pool manager via FillRewards rather than BankMsg

[kaimen-sano]

Description and Motivation

We currently use BankMsg::Send when a swap has occurred to send the protocol fees to the whale-lair. This is not desired, as it does not allow the whale-lair contract to hook into receiving the assets.

Related Issues

Closes #312.

Adding a integration test for this behaviour this is hard due to https://github.com/CosmWasm/cw-plus/issues/763. Unfortunately the cosmwasm team is not interested in addressing this issue.

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Checklist:

• [X] I have read Migaloo's contribution guidelines.
• [X] My pull request has a sound title and description (not something vague like Update index.md)
• [X] All existing and new tests are passing.
• [X] I updated/added relevant documentation.
• [X] The code is formatted properly cargo fmt --all --.
• [X] Clippy doesn't report any issues cargo clippy -- -D warnings.
• [X] I have regenerated the schemas if needed cargo schema.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.50%. Comparing base (a8ebb95) to head (e180cc6). Report is 1 commits behind head on release/v2_contracts.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release/v2_contracts #334 +/- ## ===================================================== Coverage 89.49% 89.50% ===================================================== Files 261 261 Lines 26646 26650 +4 ===================================================== + Hits 23848 23852 +4 Misses 2798 2798 ```

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