Update PluginStats with new field in response optional_extended_plugins

[cwperks]

Description

A new field was added to the output of the response to GET _cat/plugins for optional_extended_plugins in 2.19.

See opensearch-project/OpenSearch#16909 (comment) and opensearch-project/opensearch-go#669

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[github-actions]

Changes Analysis

Commit SHA: 0758d80
Comparing To SHA: 22483a2

API Changes

Summary

└─┬Components
  └─┬_common___PluginStats
    ├──[➕] required (35631:11)❌ 
    └──[➕] properties (35619:9)

Document Element	Total Changes	Breaking Changes
components	2	1

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

Report

The full API changes report is available at: https://github.com/opensearch-project/opensearch-api-specification/actions/runs/13298096671/artifacts/2582663002

API Coverage

	Before	After	Δ
Covered (%)	663 (64.94 %)	663 (64.94 %)	0 (0 %)
Uncovered (%)	358 (35.06 %)	358 (35.06 %)	0 (0 %)
Unknown	45	45	0

[dblock]

See tests failing please.

Any way we can actually test this field in a response? We have a way to install plugins, you can inspire yourself from https://github.com/opensearch-project/opensearch-api-specification/tree/main/tests/plugins.

Update https://github.com/opensearch-project/opensearch-api-specification/blob/main/.github/workflows/test-spec.yml to use 2.19 as stable (replace all 2.18s). Use a 2.20 (even thought there's no plan for such a thing) from dockerhub for the next version.

[cwperks]

See tests failing please.

Any way we can actually test this field in a response? We have a way to install plugins, you can inspire yourself from https://github.com/opensearch-project/opensearch-api-specification/tree/main/tests/plugins.

Update https://github.com/opensearch-project/opensearch-api-specification/blob/main/.github/workflows/test-spec.yml to use 2.19 as stable (replace all 2.18s). Use a 2.20 (even thought there's no plan for such a thing) from dockerhub for the next version.

There is an existing GET _cat/plugins test, but the only assertion is 200 for the status code of the response.

I'll see if I can strengthen the existing assertion.

[cwperks]

Is the default test group supposed to contain tests for knn plugin?

ERROR   knn/models.yaml (tests/default/knn/models.yaml)
    ERROR   PROLOGUES
        PASSED  PUT /movies
        PASSED  POST /_bulk
        ERROR   POST /_plugins/_knn/models/model-1/_train (Validation Failed: 1: Number of training points should be greater than 1000;)

ref: https://github.com/opensearch-project/opensearch-api-specification/actions/runs/13298096662/job/37134385075?pr=814