Add release notes (#301)

RELEASE_NOTES.md

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+## What's Changed
+* Add release notes by @byte-bandit in https://github.com/palomachain/pigeon/pull/291
+* Revert "Add release notes" by @byte-bandit in https://github.com/palomachain/pigeon/pull/292
+* Bump github.com/go-resty/resty/v2 from 2.8.0 to 2.9.1 by @dependabot in https://github.com/palomachain/pigeon/pull/296
+* Bump google.golang.org/grpc from 1.58.1 to 1.58.2 by @dependabot in https://github.com/palomachain/pigeon/pull/286
+* Bump github.com/onsi/gomega from 1.27.10 to 1.28.0 by @dependabot in https://github.com/palomachain/pigeon/pull/294
+* Update README.md by @byte-bandit in https://github.com/palomachain/pigeon/pull/297
+* fix: avoid retries on already executed messages by @byte-bandit in https://github.com/palomachain/pigeon/pull/298
+* fix: filter gravity batches queried from paloma by @byte-bandit in https://github.com/palomachain/pigeon/pull/299
+* chore: avoid error swallowing by @byte-bandit in https://github.com/palomachain/pigeon/pull/300
+
+
+**Full Changelog**: https://github.com/palomachain/pigeon/compare/v1.9.0...v1.9.1