[VS Incentives]: more CreateGroup and Distribute test cases

[p0mvn]

We need more CreateGroup and Distribute test cases

Namely:

• Test_Distribute_Group_OverlappingPoolsInGroups - two groups, distribute to the same gauges, assert distributions are as expected
• Test_Distribute_Group_NoVolumeOnePool_SkipSilent - two groups, one has no volume, assert that it is silently skipped but other distributes
• Test_Distribute_Group_ChangeVolumeBetween - two groups distribute over 2 epochs, volume changed between epochs
• Test_Distribute_Group_CreateGroupsBetween - start with one group at epoch, add another group at second epoch
• Test_Distribute_Group_SwapAndDistribute - update volume by swapping instead of setting state directly and then distribute

Originally posted by @p0mvn in #6548 (comment)

A/C

• All tests are added