adding rank_eval indices API tests

[Tokesh]

Description

test for:
GET /_rank_eval
POST /_rank_eval
GET /{index}/_rank_eval
POST /{index}/_rank_eval

Issues Resolved

[#663 ]

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[github-actions]

Changes Analysis

Commit SHA: 866897a
Comparing To SHA: 3981d33

API Changes

Summary

└─┬Components
  ├─┬_core.rank_eval___RankEvalMetricDetail
  │ └─┬metric_details
  │   └─┬Schema
  │     └─┬Schema
  │       └──[🔀] type (43394:21)❌ 
  └─┬_core.rank_eval___RankEvalHit
    └──[➕] properties (43335:9)

Document Element	Total Changes	Breaking Changes
components	2	1

• ❌ BREAKING Changes: 1 out of 2
• Modifications: 1
• Additions: 1
• Breaking Modifications: 1

Report

The full API changes report is available at: https://github.com/opensearch-project/opensearch-api-specification/actions/runs/12146406371/artifacts/2269346061

API Coverage

	Before	After	Δ
Covered (%)	599 (58.67 %)	599 (58.67 %)	0 (0 %)
Uncovered (%)	422 (41.33 %)	422 (41.33 %)	0 (0 %)
Unknown	42	42	0

[dblock]

1.3.x returns _type in the docs, schema should be referencing an existing document model somewhere

[github-actions]

Spec Test Coverage Analysis

Total	Tested
528	423 (80.11 %)

[Tokesh]

I think its ready for review, open to any suggestions :)
We have achieved 80% test coverage!
We're almost there—100% coverage is within reach!

[dblock]

So these are always numbers?

[Tokesh]

I'll try to read it in the future, most likely yes.
If I notice it's not, I'll open a new pull request.