add 2.0-rc1 release notes (opensearch-project#295)

Signed-off-by: Xun Zhang <[email protected]>

Author: Zhangxunmt

release-notes/opensearch-ml-common.release-notes-2.0.0.0-rc1.md

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+## Version 2.0.0.0-rc1 Release Notes
+
+Compatible with OpenSearch 2.0.0-rc1
+
+### Enhancements
+
+* Add circuit breaker trigger count stat.([#274](https://github.com/opensearch-project/ml-commons/pull/274))
+
+### Bug Fixes
+
+* support dispatching execute task; don't dispatch ML task again ([#279](https://github.com/opensearch-project/ml-commons/pull/279))
+* Fix NPE in anomaly localization ([#280](https://github.com/opensearch-project/ml-commons/pull/280))
+* create model/task index with correct mapping ([#284](https://github.com/opensearch-project/ml-commons/pull/284))
+
+### Infrastructure
+
+* drop support for JDK 14 ([#267](https://github.com/opensearch-project/ml-commons/pull/267))
+* Add UT/IT Coverage for action/models and action/tasks. ([#268](https://github.com/opensearch-project/ml-commons/pull/268))
+* Default qualifier to alpha1 and fix workflows ([#269](https://github.com/opensearch-project/ml-commons/pull/269))
+* Remove additional vars in build.gradle that are not used ([#271](https://github.com/opensearch-project/ml-commons/pull/271))
+* Add UT for Search transport action. ([#272](https://github.com/opensearch-project/ml-commons/pull/272))
+* updated issue templates for bugs and features. ([#273](https://github.com/opensearch-project/ml-commons/pull/273))
+* Add more test to improve coverage of abstract search action([#275](https://github.com/opensearch-project/ml-commons/pull/275))
+* Add UT for RestMLExecuteAction, and remove it out from the jacoco exclusive list. ([#278](https://github.com/opensearch-project/ml-commons/pull/278))
+* add coverage badges ([#281](https://github.com/opensearch-project/ml-commons/pull/281))
+* Re-enable docker image tests for 2.0. ([#288](https://github.com/opensearch-project/ml-commons/pull/288))
+
+### Maintenance
+
+* Change 2.0-alpha1 to 2.0-rc1. ([#282](https://github.com/opensearch-project/ml-commons/pull/282))
+* bump RCF version to 3.0-rc2.1 ([#289](https://github.com/opensearch-project/ml-commons/pull/289))
+
+### Refactoring
+
+* Removed RCF jars and updated to fetch RCF 3.0-rc2 from maven ([#277](https://github.com/opensearch-project/ml-commons/pull/277))
+