chore: add release notes to v2.2.1

RELEASE_NOTES.md

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+## What's Changed
+
+* feat: add pigeon metrics to telemetry endpoint by @maharifu in https://github.com/palomachain/paloma/pull/1287
+* chore: update skyway validator nonces by @maharifu in https://github.com/palomachain/paloma/pull/1288
+* feat: endpoint to query open skyway attestations by @maharifu in https://github.com/palomachain/paloma/pull/1289
+* feat: add authz module by @maharifu in https://github.com/palomachain/paloma/pull/1290
+* chore: ignore claims behind last observed nonce by @maharifu in https://github.com/palomachain/paloma/pull/1291
+* chore: update validator nonces in endblocker by @maharifu in https://github.com/palomachain/paloma/pull/1292
+* chore: update README to v2.2.1 by @maharifu in https://github.com/palomachain/paloma/pull/1293
+
+
+**Full Changelog**: https://github.com/palomachain/paloma/compare/v2.2.0...v2.2.1