Document that APM Server OTLP is not recommended for new users; recommend EDOT Collector / Managed OTLP

[alexandra5000]

Summary

Updates APM Server docs to state that the OTLP endpoint on APM Server is not recommended for new users and to direct new users to the OpenTelemetry path using the EDOT Collector or Managed OTLP instead.

EDOT SDKs not supported through APM Server has already been documented in the troubleshooting EDOT SDKs page, OpenTelemetry limitations, and (now clearly) in the OpenTelemetry intake API callout.

Close #1198

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

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• No

2. If you answered "Yes" to the previous question, please specify the tool(s) and model(s) used (e.g., Google Gemini, OpenAI ChatGPT-4, etc.).

Tool(s) and model(s) used: Claude 4.5 using Cursor

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Vale Linting Results

Summary: 1 suggestion found

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File	Line	Rule	Message
solutions/observability/apm/opentelemetry-intake-api.md	20	Elastic.Semicolons	Use semicolons judiciously.

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🔍 Preview links for changed docs

• solutions/observability/apm/apm-server/api.md
• solutions/observability/apm/apm-server/index.md
• solutions/observability/apm/opentelemetry-intake-api.md