Remove references to buildkite (cadence-workflow#1014)

Co-authored-by: Mandy Chen <[email protected]>

Author: 2 people

.buildkite/pipeline.yml

@@ -97,5 +97,5 @@ And sometimes it's important to test the non-sticky mode
 STICKY_OFF=true USE_DOCKER_SERVICE=true ./gradlew test
 ```
 
-Also, if there is any Buildkite test failure that you cannot reproduce locally, 
-follow [buildkite docker-compose](./docker/buildkite/README.md) instructions to run the tests.
+Also, if there is any Github Actions test failure that you cannot reproduce locally, 
+follow [github action docker-compose](./docker/github_actions/README.md) instructions to run the tests.

.buildkite/scripts/coverage_metadata.sh

@@ -1,4 +1,4 @@
-# Java framework for Cadence [![Build Status](https://badge.buildkite.com/0c96b8b74c0921208e898c10a602e2fe9ecb7641c2befee0e7.svg?theme=github&branch=master)](https://buildkite.com/uberopensource/cadence-java-client) [![Javadocs](https://www.javadoc.io/badge/com.uber.cadence/cadence-client.svg)](https://www.javadoc.io/doc/com.uber.cadence/cadence-client) [![codecov](https://codecov.io/gh/cadence-workflow/cadence-java-client/graph/badge.svg?token=eVBGf4EmXr)](https://codecov.io/gh/cadence-workflow/cadence-java-client)
+# Java framework for Cadence [![CI Checks](https://github.com/cadence-workflow/cadence-java-client/actions/workflows/ci-checks.yml/badge.svg)](https://github.com/cadence-workflow/cadence-java-client/actions/workflows/ci-checks.yml) [![Javadocs](https://www.javadoc.io/badge/com.uber.cadence/cadence-client.svg)](https://www.javadoc.io/doc/com.uber.cadence/cadence-client) [![codecov](https://codecov.io/gh/cadence-workflow/cadence-java-client/graph/badge.svg?token=eVBGf4EmXr)](https://codecov.io/gh/cadence-workflow/cadence-java-client)
 
 
 [Cadence](https://github.com/uber/cadence) is a distributed, scalable, durable, and highly available orchestration engine we developed at Uber Engineering to execute asynchronous long-running business logic in a scalable and resilient way.