Operational how-to: OpenTelemetry configuration

[khuyentran1401]

Sub-issue of #630.

Scope

A how-to for configuring OpenTelemetry export from nic and the Nebari Operator.

New page under docs/docs/how-tos/.

Content:

• OTEL_EXPORTER env var
• OTEL_ENDPOINT env var
• Console vs OTLP vs dual export
• Sending traces to a local collector

Cross-links:

• Architecture explainer (Conceptual docs: NKP architecture explainer #625)

Acceptance criteria

• Page includes concrete commands, not just prose
• Page notes NKP-only scope (Classic equivalent stays under /classic/ if present)
• Cross-links wired

Reference

Repos:

• nic CLI: https://github.com/nebari-dev/nebari-infrastructure-core

Source in nebari-infrastructure-core:

• Telemetry: pkg/telemetry/telemetry.go