feat: Add convenience method for constructing key to access account's…

… balance for a given denom (backport cosmos#12674) (cosmos#12744)

* feat: Add convenience method for constructing key to access account's balance for a given denom (cosmos#12674)

This PR adds a convenience method for constructing the key necessary to query for the account's balance of a given denom.

I ran into this issue since we are using ABCI query now to perform balance requests because we are also requesting merkle proofs for the returned balance [here](https://github.com/celestiaorg/celestia-node/pull/911/files#diff-0ee31f5a7bd88e9f758e6bebdf3ee36365519e55a451098d9638c39afe5eac42R144).

It would be nice to have a definitive convenience method for constructing the key.

[Ref.](github.com/celestiaorg/celestia-node/pull/911)

(cherry picked from commit a1777a8)

* updates changelog

Co-authored-by: rene <41963722+renaynay@users.noreply.github.com>
Co-authored-by: Julien Robert <julien@rbrt.fr>

CHANGELOG.md

@@ -36,6 +36,12 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 # Changelog
 
+## [Unreleased]
+
+### Improvements
+
+* (x/bank) [#12674](https://github.com/cosmos/cosmos-sdk/pull/12674) Add convenience function `CreatePrefixedAccountStoreKey()` to construct key to access account's balance for a given denom.
+
 ## [v0.46.0](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.46.0) - 2022-07-26
 
 ### Features