[rule based autotagging] Add Get Rule API Logic

[ruai0511]

Description

This PR introduces the get Rule API Logic.

An example API request is:

curl -XGET "localhost:9200/_wlm/rule" // get all rules
curl -XGET "localhost:9200/_wlm/rule/{_id}" // get single rule by id
curl -XGET "localhost:9200/_wlm/rule?index_pattern=a,b" // get all rules containing index_pattern as a or b 

And the return would be

{
   "rules":[
      {
         "_id":"LN1z8pQBW57iKqfUCG6A",
         "index_pattern":[
            "logs*",
            "events*"
         ],
         "query_group":"dev_query_group_id_2",
         "updated_at":"2025-02-11T00:40:12.671Z"
      },
      ...
   ]
}

Rule Schema PR:
#17238
RFC:
#16797

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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❌ Gradle check result for db57bcb: FAILURE

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✅ Gradle check result for 783ce61: SUCCESS

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❌ Gradle check result for 9087c7f: FAILURE

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[jainankitk]

Unrelated failures, retrying gradle check:

[Test Result](https://build.ci.opensearch.org/job/gradle-check/56957/testReport/) (1 failure / -5)

    [org.opensearch.rest.ReactorNetty4StreamingStressIT.testCloseClientStreamingRequest](https://build.ci.opensearch.org/job/gradle-check/56957/testReport/junit/org.opensearch.rest/ReactorNetty4StreamingStressIT/testCloseClientStreamingRequest/)

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❌ Gradle check result for 9087c7f: FAILURE

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✅ Gradle check result for 14237d2: SUCCESS

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✅ Gradle check result for f1f2108: SUCCESS

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✅ Gradle check result for d6b3e79: SUCCESS