add 1.8.2 release changelog

RELEASE_CHANGELOG.md

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+## [v1.8.2](https://github.com/provenance-io/provenance/releases/tag/v1.8.2) - 2022-04-22
+
+### Summary
+
+Provenance 1.8.2 is a point release to fix an issue with "downgrade detection" in Cosmos SDK. A panic condition 
+occurs in cases where no update handler is found for the last known upgrade, but the process for determining
+the last known upgrade is flawed in Cosmos SDK 0.45.3. This released uses an updated Cosmos fork to patch the
+issue until an official patch is released. Version 1.8.2 also adds some remaining pieces for  ADR-038 that were 
+missing in the 1.8.1 release.
+
+### Bug Fixes
+
+* Order upgrades by block height rather than name to prevent panic [\#106](https://github.com/provenance-io/cosmos-sdk/pull/106)
+
+### Improvements
+
+* Add remaining updates for ADR-038 support [\#786](https://github.com/provenance-io/provenance/pull/786)