[BUG] plugins.ppl.enabled setting is not working when it is set in opensearch.yml

[vmmusings]

What is the bug?
plugins.ppl.enabled setting mentioned in opensearch.yml is not working. However, it is working when it is updated through settings API.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. set plugins.ppl.enabled: false in opensearch.yml.
2. Hit ppl api with any query. Although ppl is disabled, ppl api gives out result.

What is the expected behavior?
When ppl is disabled in opensearch.yml, opensearch shouldn't allow any ppl requests.

What is your host/environment?

• OS: Mac
• Version 3.0.0
• Plugins opensearch-sql.

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Do you have any additional context?
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