Support withdraw authorizations on markers

[iramiller]

Summary

Provide support in the marker module for delegation of withdraw from a marker with a specific total allocation.

Problem Definition

With the new authz module there are numerous applications for delegation and control within the marker module. In addition to the #265 support for transfer delegation the ability to delegate specific withdraw capability would also be useful. This authorization would allow an administrator with the withdraw permission to create an authorization grant for another account with a specific maximum amount that can be removed from escrow.

Proposal

• Create an authz configuration that supports withdrawing specific coin balances from a marker "escrow" account.

One way this can be implemented via a custom endpoint on the marker module that allows a caller with withdraw access on a marker to submit a request that will generate a standard authz grant as if it were signed/submitted by the marker account address itself.

• Include support for creating "feegrants" against the marker escrow balance such that other accounts can use the escrow to cover gas costs. Require the "admin" role to create this grants instead of the "withdraw" role given the indirect nature of the use of funds.

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