feat(x/ecocredit): forward contract API

[aaronc]

Description

This adds an API which allows project admins to issue forward contract batches for their project which are not linked to any credit class and have no credit type nor start/end dates, but otherwise function like regular credit batches with respect to the marketplace and other functionality.

This strategy distinctly from approaches we consider earlier, makes zero assumptions about how credits will be fulfilled. The only requirement would be that forward contracts get "retired". This has the advantage of making it easier to deploy this functionality because we don't need to get the requirements of relating forwards to credits correctly and can have lots of flexibility off chain. But it does impose the limitation that this functionality doesn't exist on chain and must be coordinated off chain

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[aaronc]

Closing in favor of #2150 which handles this via multiple credit classes per project.