[8.19](backport #50492) x-pack/filebeat/input/streaming: apply configured timeout to OAuth2 token requests

[mergify]

Proposed commit message

x-pack/filebeat/input/streaming: apply configured timeout to OAuth2 token requests

The CrowdStrike FalconHose input constructed the OAuth2 HTTP client
with only the Transport from the auth client, dropping the Timeout
set by httpcommon.HTTPTransportSettings. Token endpoint requests
could hang indefinitely instead of respecting the configured timeout.

Apply the timeout via context.WithTimeout in rateLimitTransport
rather than http.Client.Timeout to avoid the deprecated
oauth2.Transport.CancelRequest path.

Also fix flaky test.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• I have added an entry in ./changelog/fragments using the changelog tool.

Disruptive User Impact

How to test this PR locally

Related issues

• Closes [bug-hunter] CrowdStrike OAuth2 auth requests ignore configured timeout #49988

Use cases

Screenshots

Logs

---

This is an automatic backport of pull request #50492 done by [Mergify](https://mergify.com).

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