Add INSTANCE_OPERATION_STATE field for easy instance state visibility

[LZD-PratyushBhatt]

Issues

• My PR addresses the following Helix issues and references them in the PR description:
  Add INSTANCE_OPERATION_STATE field for easy instance state visibility

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Description

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

(Write a concise description including what, why, how)
Currently, customers find it difficult to understand the actual active instance operation state from InstanceConfig JSON.

This commit adds a new simple field INSTANCE_OPERATION_STATE that shows the current active instance operation state as a plain string value (ENABLE, DISABLE, EVACUATE, SWAP_IN, or UNKNOWN).

Tests

UTs added + Manually tested.

1. If a new instance is added, its intial config gets this field set:

{
  "id" : "localhost_12225",
  "simpleFields" : {
    "HELIX_HOST" : "localhost",
    "HELIX_PORT" : "12225",
    "INSTANCE_OPERATION_STATE" : "ENABLE"
  },
  "mapFields" : { },
  "listFields" : { }
}

2. setIntanceOperationAPI updates the field as well.

{
  "id" : "localhost_12223",
  "simpleFields" : {
    "HELIX_DISABLED_REASON" : "enable",
    "HELIX_ENABLED" : "false",
    "HELIX_ENABLED_TIMESTAMP" : "1763570965923",
    "HELIX_HOST" : "localhost",
    "HELIX_PORT" : "12223",
    "INSTANCE_OPERATION_STATE" : "UNKNOWN"
  },
  "mapFields" : { },
  "listFields" : {
    "HELIX_INSTANCE_OPERATIONS" : [ "{\"OPERATION\":\"ENABLE\",\"TIMESTAMP\":\"1763570941008\",\"SOURCE\":\"ADMIN\",\"REASON\":\"enable\"}", "{\"OPERATION\":\"DISABLE\",\"TIMESTAMP\":\"1763570965923\",\"SOURCE\":\"AUTOMATION\",\"REASON\":\"enable\"}", "{\"OPERATION\":\"UNKNOWN\",\"TIMESTAMP\":\"1763570987431\",\"SOURCE\":\"USER\",\"REASON\":\"enable\"}" ]
  }
}

• The following tests are written for this issue:

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Changes that Break Backward Compatibility (Optional)

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

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Documentation (Optional)

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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")
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Code Quality

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

[proud-parselmouth]

LGTM.

[proud-parselmouth]

nit: call updateInstanceOperationState again here