[VS Incentives] feat: non-perpetual Group & group Gauge pruning

[p0mvn]

We need to make sure that Group's lifecycle is the same as the underlying gauge lifecycle.

That is, if a Group is finished, the 1:1 mapped group's gauge is also finished

Originally posted by @p0mvn in #6431 (comment)

Suggested Design

For speed of delivery, I propose the following:

• Write groups to a separate store index
• Write group gauges into a regular gauge index but do not create upcoming/active/finished ref keys
• In distribution logic, get all groups present, iterate over them and retrieve the associated group gauges
• At the end of the distribution logic, prune non-perpetual expired gauges and groups. If any dust remaining, send to community pool
• Restrict external incentive providers to only be able to create non-perpetual gauges so that it is impossible to create permanent perpetual junk even with the fee
  • This is consistent with the fact that most external are non-perpetual anyways
    please correct me if not
• Give subdao powers to remove perpetual gauges that have no use via a special message (alternatively, gov prop)

This PR focuses specifically on pruning of non-perpetual gauges.

A/C

• Implement method for pruning non-perpetual groups and group gauges
• Integrate into AllocateAcrossGauges
• Test both methods
• Review this PR's links to this issue to make sure that all TODOs are addressed: [VS Incentives]: Update AllocateAcrossGauges to support volume splitting #6431
• In particular, update these TODOs:
  • [VS Incentives]: Update AllocateAcrossGauges to support volume splitting #6431 (comment)
  • [VS Incentives]: Update AllocateAcrossGauges to support volume splitting #6431 (comment)
  • [VS Incentives]: Update AllocateAcrossGauges to support volume splitting #6431 (comment)

[p0mvn]

TODO:
submit removal of boolean parameter from CreateGaugeRefKeys via separate PR

[p0mvn]

Realized that it is impossible to write group gauges into a separate store index from regular gauges since we rely on the group gauge to be written into regular gauge index in pool incentives distribution.

Also, upcoming / active / finished ref keys aren't needed for group gaugs since we will:

• allow external incentive providers to only create non-perpetual group gauges that get pruned on completion
• create subdao that has powers to delete unused perpetual group gauges