doc: add warning for otlp over grpc

[verysonglaa]

Description

After hours of troubleshooting I discovered that the opentelemetry collector service in my cluster does not follow the istio port naming convention. Adding a warning to the opentelemetry task to help others running into the same situation.

Reviewers

• [ ] Ambient
• [x] Docs
• [ ] Installation
• [ ] Networking
• [ ] Performance and Scalability
• [ ] Extensions and Telemetry
• [ ] Security
• [ ] Test and Release
• [ ] User Experience
• [ ] Developer Infrastructure
• [ ] Localization/Translation

[istio-policy-bot]

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[linux-foundation-easycla[bot]]

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• :white_check_mark: login: verysonglaa (99a17d8a94329a0e1fbdbaf1e164b8ee28c00f49, ed874f42f1ccc8d77fd6cb6038fd4e3db0958cb5)

[istio-testing]

Hi @verysonglaa. Thanks for your PR.

I'm waiting for a istio member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[verysonglaa]

/retest