Replace master terminology in documentation

[xuezhou25]

Description

Replace non-inclusive word "master" in *.md documentation file.

Issues Resolved

Close #2694

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[tlfeng]

Thanks for changing the non-inclusive term. 👍

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/1230/
• CommitID: 1b4513f275dab20239f1c2e479c75790f68f3001

[dreamer-89]

Do we need to replace master (value above) as well ?

[xuezhou25]

Yes. Changed it

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/1236/
• CommitID: cff7cfe

[tlfeng]

In build 1236:

REPRODUCE WITH: ./gradlew ':server:test' --tests "org.opensearch.search.DeletePitMultiNodeTests.testDeletePitWhileNodeDrop" -Dtests.seed=9E251EB37CB6899A -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=es-HN -Dtests.timezone=Australia/Lord_Howe -Druntime.java=17

org.opensearch.search.DeletePitMultiNodeTests > testDeletePitWhileNodeDrop FAILED
    java.lang.AssertionError
        at __randomizedtesting.SeedInfo.seed([9E251EB37CB6899A:6388D672E32212A0]:0)
        at org.junit.Assert.fail(Assert.java:87)
        at org.junit.Assert.assertTrue(Assert.java:42)
        at org.junit.Assert.assertFalse(Assert.java:65)
        at org.junit.Assert.assertFalse(Assert.java:75)
        at org.opensearch.search.DeletePitMultiNodeTests$1.onNodeStopped(DeletePitMultiNodeTests.java:184)
        at org.opensearch.test.InternalTestCluster$NodeAndClient.closeForRestart(InternalTestCluster.java:1028)
        at org.opensearch.test.InternalTestCluster.restartNode(InternalTestCluster.java:1931)
        at org.opensearch.test.InternalTestCluster.restartRandomDataNode(InternalTestCluster.java:1879)
        at org.opensearch.search.DeletePitMultiNodeTests.testDeletePitWhileNodeDrop(DeletePitMultiNodeTests.java:176)

It's not related to the code change in this PR.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/1237/
• CommitID: cff7cfe