docs(inputs.kubernetes): Remove stale bearer_token_string documentation

[ldv8434]

Summary

The bearer_token_string configuration field is no longer used in the kubernetes input plugin. From what I can tell, it was removed in #17109 but the documentation still includes it as an option.

This pull request removes the references to the bearer_token_string field.

Checklist

• No AI generated code was used in this PR
• AI generated code used in this PR follows the InfluxData Policy on AI-Generated Code Contributions

Related issues

resolves #18673

[telegraf-tiger]

Thanks so much for the pull request!
🤝 ✒️ Just a reminder that the CLA has not yet been signed, and we'll need it before merging. Please sign the CLA when you get a chance, then post a comment here saying !signed-cla

[ldv8434]

!signed-cla

[skartikey]

@ldv8434 Thanks for the fix! The README is generated from plugins/inputs/kubernetes/sample.conf via make docs, so editing the README directly will get overwritten. Please update sample.conf instead, then run make docs to regenerate the README. That should also fix the lint-linux CI failure.

[ldv8434]

Thanks for the heads-up! Fixed, pushed, and it looks like it passed the CI!

[skartikey]

@ldv8434 Thanks for the contribution!

[srebhan]

Thanks @ldv8434!