[Feature]: add multimsg execution to x/accounts' base account

[testinginprod]

Summary

Add multimsg execution to base account of x/accounts module

Problem Definition

Serverv2 does not allow multimsgs in txs, so we need to shift this functionality to the account itself.

Proposed Feature

Add multimsg execution to base account, also support custom atomicity.

[julienrbrt]

I think the description is wrong, you can submit a tx with multiple messages. I don't think it is an x/accounts concern either.
The issue is multiple txs in the same block.

[tac0turtle]

dont think we need this, there was confusion