chore: 0.45.7 changelog prep (cosmos#12821)

* prepare for release

* modify release notes

CHANGELOG.md

@@ -35,7 +35,9 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 # Changelog
 
-## [Unreleased]
+## Unreleased
+
+## v0.45.7 - 2022-08-04
 
 ### Features
 
@@ -46,6 +48,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (x/params) [#12724](https://github.com/cosmos/cosmos-sdk/pull/12724) Add `GetParamSetIfExists` function to params `Subspace` to prevent panics on breaking changes.
 * [#12668](https://github.com/cosmos/cosmos-sdk/pull/12668) Add `authz_msg_index` event attribute to message events emitted when executing via `MsgExec` through `x/authz`.
 * [#12697](https://github.com/cosmos/cosmos-sdk/pull/12697) Upgrade IAVL to v0.19.0 with fast index and error propagation. NOTE: first start will take a while to propagate into new model.
+  - Note: after upgrading to this version it may take up to 15 minutes to migrate from 0.17 to 0.19. This time is used to create the fast cache introduced into IAVL for performance
 * [#12784](https://github.com/cosmos/cosmos-sdk/pull/12784) Upgrade Tendermint to 0.34.20. 
 * (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.
 

RELEASE_NOTES.md

@@ -1,9 +1,10 @@
-# Cosmos SDK v0.45.6 Release Notes
+# Cosmos SDK v0.45.7 Release Notes
 
-This release introduces a few bug fixes and improvements.
-Notably, it fixes `GetLastCompleteUpgrade` in `x/upgrade` to properly return the latest upgrade.
+This release introduces a few bug fixes, improvements and updated Tendermint and IAVL dependencies.
 
-See the [Cosmos SDK v0.45.6 Changelog](https://github.com/cosmos/cosmos-sdk/blob/v0.45.6/CHANGELOG.md)
+> Note: When using 0.45.7, the restart of the binary could take up to 15 minutes in order to build the fast cache of IAVL. The fast cache will provide a performance improvement over 0.45.6.
+
+See the [Cosmos SDK v0.45.7 Changelog](https://github.com/cosmos/cosmos-sdk/blob/v0.45.7/CHANGELOG.md)
 for the exhaustive list of all changes.
 
-**Full Commit History**: https://github.com/cosmos/cosmos-sdk/compare/v0.45.5...v0.45.6
+**Full Commit History**: https://github.com/cosmos/cosmos-sdk/compare/v0.45.6...v0.45.7