Add REST APIs for management mode

[huizhilu]

Issues

• My PR addresses the following Helix issues and references them in the PR description:

Resolves #1741

Description

• Here are some details about my PR, including screenshots of any UI changes:

Helix provides JAVA and REST APIs to set management mode and get the management mode status.
This PR adds a java api to get management status in HelixAdmin:
ClusterManagementMode getClusterManagementMode(String clusterName)

REST APIs:

POST /clusters/<cluster>/management-mode

GET  /clusters/myCluster/management-mode
QueryParam: showDetails

Examples:

POST /clusters/<cluster>/management-mode -d \
'{
  "mode": "CLUSTER_FREEZE",
  "cancelPendingST": false,
  "reason": "Freeze cluster for maintenance and let pending ST finish"
}'
 
Status: 200
{
    "acknowledged": true
}

GET  /clusters/myCluster/management-mode 
// Sample 1: Fully frozen. No pending state transitions.
{
    "cluster": "myCluster",
    "mode": "CLUSTER_FREEZE",
    "status": "COMPLETED"
}


GET  /clusters/myCluster/management-mode?showDetails=true
{
  "cluster": "myCluster",
  "mode": "CLUSTER_FREEZE",
  "status": "IN_PROGRESS",
  "details": {
    "cluster": {
      "cluster": "myCluster",
      "status": "IN_PROGRESS"
    },
    "liveInstances": {
      "status": "IN_PROGRESS",
      "hasPendingStateTransition": false,
      "liveInstancesInProgress": [
        "node-1",
        "node-2"
      ]
    }
  }
}

Tests

• The following tests are written for this issue:

TestClusterAccessor#testClusterFreezeMode

• The following is the result of the "mvn test" command on the appropriate module:

17:27:24,990 [INFO] Tests run: 179, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 97.365 s - in TestSuite
17:27:25,437 [INFO]
17:27:25,437 [INFO] Results:
17:27:25,437 [INFO]
17:27:25,438 [INFO] Tests run: 179, Failures: 0, Errors: 0, Skipped: 0
17:27:25,438 [INFO]
17:27:25,445 [INFO]
17:27:25,445 [INFO] --- jacoco-maven-plugin:0.8.6:report (generate-code-coverage-report) @ helix-rest ---
17:27:25,480 [INFO] Loading execution data file /home/hulu/Projects/helix/helix-rest/target/jacoco.exec
17:27:25,633 [INFO] Analyzed bundle 'Apache Helix :: Restful Interface' with 79 classes
17:27:25,882 [INFO] ------------------------------------------------------------------------
17:27:25,883 [INFO] BUILD SUCCESS
17:27:25,883 [INFO] ------------------------------------------------------------------------
17:27:25,884 [INFO] Total time:  01:44 min
17:27:25,885 [INFO] Finished at: 2021-06-28T17:27:25-07:00
17:27:25,885 [INFO] ------------------------------------------------------------------------

Changes that Break Backward Compatibility (Optional)

• My PR contains changes that break backward compatibility or previous assumptions for certain methods or API. They include:

(Consider including all behavior changes for public methods or API. Also include these changes in merge description so that other developers are aware of these changes. This allows them to make relevant code changes in feature branches accounting for the new method/API behavior.)

Documentation (Optional)

• In case of new functionality, my PR adds documentation in the following wiki page:

(Link the GitHub wiki you added)

Commits

• My commits all reference appropriate Apache Helix GitHub issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Code Quality

• My diff has been formatted using helix-style.xml
  (helix-style-intellij.xml if IntelliJ IDE is used)

[alirezazamani]

LGTM

[huizhilu]

This PR is ready to be merged, approved by @alirezazamani