[VS Incentives]: Refactor CreateGroupGauge to take in a list of pool IDs instead of gauge IDs

[AlpinYukseloglu]

Background

Since group gauge logic heavily leans on there being a pool linked to each internal gauge and since we want the top level message to take in a list of pool IDs to split between, CreateGroupGauge should be refactored to take in a list of pool IDs instead of gauge IDs. This could likely be done in conjunction with #6401, which also deals with pool IDs.

Suggested Design

• Replace gauge list input with pool ID list and initialize gauge using function implemented in [VS Incentives]: Implement initGaugeInfo helper #6401. Then, sync gauge weights using syncGroupGaugeWeights and test the function

Acceptance Criteria

• Group gauge creation logic is complete and well tested
• Test skips and TODOs are removed from relevant tests in x/incentives/keeper/gauge_test.go