Add support for feegrant pruning

[robert-zaremba]

Summary

Similarly to x/authz we should enable feegrant objects auto-prunning using an index (similarly as we move / delete proposals in x/gov).

Ref:

• fix(authz)!: prunning: unable to execute authorization #10633
• x/authz pruning and gas #8311 (comment)

cc: @aleem1314

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