Document the OTel Collector details view in Fleet

[vishaangelova]

Summary

This PR documents the redesigned OTel Collector view in Fleet, which replaces the classic Agent details view for OpAMP-managed collectors in 9.5. The feature is gated behind the enableOtelUI flag, which is absent in 9.4 and enabled by default in 9.5.0.

Because 9.4 uses the classic Agent details view, view-otel-collectors.md documents both, but is now organized by task, with row-level applies_to badges in the metadata table and applies-switch blocks for the two divergent navigation paths.

Resolves #7412

Changes

• reference/fleet/view-otel-collectors.md (rewrite): Restructured into task-oriented sections (also making this a how-to). New coverage for the pipeline graph (selector, layout, connector edges, canvas controls), the component detail panel (Health, Metrics, Config tabs, including the internal-telemetry prerequisite for metrics), and the Error patterns table. Health states are now documented per version: named states with color indicators on 9.5, raw OTel status strings on 9.4, plus the 9.5 "Collector is not active" behavior. The metadata table merges both versions into one table with row-level badges.
• reference/fleet/add-otel-collector.md: Aligns the Start the collector tab labels with the UI and adds a 9.5-badged paragraph for the runtime selector that swaps the command. Adds a 9.5-badged note for the managed OTLP endpoint path, where the step asks for an mOTLP API key and the generated config exports through otlp/managed instead of elasticsearch/otel. Corrects the confirmation step, which names View connected collectors.
• reference/fleet/monitor-otel-collectors.md: Adds a badged paragraph pointing at the new collector details view.

Corrections to existing content

Fixes to existing content on the view-otel-collectors.md page:

• Tags: The page said collectors are tagged elastic-otel-collector or otel-contrib according to collector type. Fleet Server derives the tag from the collector's service.name attribute (internal/pkg/api/handleOpAMP.go), which is the Service name from the Add collector flow. elastic-otel-collector is just what Elastic Agent in OTel mode happens to report.
• Filtering by policy: There is no "OpAMP filter option". Fleet auto-creates a hidden managed policy named OpAMP and enrolls every collector into it; the policy is absent from the Agent policies tab but appears in the filter.

Generative AI disclosure

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

• Yes
• 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: Cursor / Claude Opus 5

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🔍 Preview links for changed docs

• reference/fleet/add-otel-collector.md
• reference/fleet/monitor-otel-collectors.md
• reference/fleet/view-otel-collectors.md

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Elastic Docs Style Checker (Vale)

Summary: 1 warning found

⚠️ Warnings (1): Fix when the suggestion improves clarity or correctness.

File	Line	Rule	Message
reference/fleet/view-otel-collectors.md	212	Elastic.Spelling	'otlp' is a possible misspelling.

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