[DOCS] Document extended spec.telemetry OTel exporter/collector fields

[inference-gateway-maintainer]

The telemetry schema shape was revised after design review, so the fields to document here have changed.

Instead of a top-level otlp block plus per-signal exporter enums, exporters are now nested under each signal following the OpenTelemetry SDK declarative-configuration model - the single key beneath exporter selects the exporter (no separate enum, no signal-agnostic protocol block):

    telemetry:
      enabled: true
      traces:
        exporter:
          otlp:
            endpoint: http://localhost:4318
            protocol: http/protobuf
      metrics:
        exporter:
          prometheus:   # pull; or otlp: to push
            host: ""
            port: 9464

• traces.exporter accepts otlp; metrics.exporter accepts otlp or prometheus; exactly one key per signal.
• Omitting a signal (or its exporter block) disables it -> OTEL_TRACES_EXPORTER=none / OTEL_METRICS_EXPORTER=none.
• Every field maps 1:1 to a standard OTEL_* env var (shared OTEL_EXPORTER_OTLP_* when both signals match, else per-signal OTEL_EXPORTER_OTLP_{TRACES,METRICS}_*).
• Headers, credentials, and sampling stay runtime-only (env), never in the manifest.

Authoritative field reference and env-var mapping table live in the ADL repo at docs/reference/telemetry.md. Schema PR: inference-gateway/adl#104 (supersedes the earlier shape in inference-gateway/adl#103).

[edenreich]

@claude Can you work on this?

[inference-gateway-maintainer]

Claude finished @edenreich's task in 8m 35s —— View job • docs/issue-397-20260715-0106 • [Create PR ➔](https://github.com/inference-gateway/docs/compare/main...docs/issue-397-20260715-0106?quick_pull=1&title=Issue%20%23397%3A%20Changes%20from%20Claude&body=This%20PR%20addresses%20issue%20%23397%0A%0AGenerated%20with%20%5BClaude%20Code%5D(https%3A%2F%2Fclaude.ai%2Fcode)

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Done - documented the revised spec.telemetry schema

The extended spec.telemetry OTel fields had no home in the docs. The ADL schema reference lives in adl-cli.md, and it had no telemetry section at all - so I added one, matching the authoritative reference (docs/reference/telemetry.md in inference-gateway/adl, schema PR adl#104, shipped in ADL v0.19.0).

• Gather context: found the ADL schema reference in adl-cli.md (not the gateway observability.md, which is env-var driven)
• Read the authoritative field reference + schema definitions from inference-gateway/adl
• Add a Telemetry section documenting the new nested-exporter shape
• Lint / format / build checks
• Commit and open PR

What changed in adl-cli.md:

• New Telemetry section under the ADL Schema Reference:
  • Per-signal traces / metrics exporters nested under exporter (OpenTelemetry SDK declarative-configuration model) - the single key beneath exporter selects it, no separate enum, no signal-agnostic protocol block.
  • traces.exporter -> otlp; metrics.exporter -> otlp (push) or prometheus (pull); exactly one per signal (oneOf); omitting a signal disables it (OTEL_*_EXPORTER=none).
  • Field tables for spec.telemetry, the per-signal exporter, and the otlp / prometheus exporters.
  • The 1:1 OTEL_* env-var mapping table (shared vs per-signal OTLP vars), plus the note that headers / credentials / sampling stay runtime-only (env), never in the manifest.
• Added a telemetry block to the Complete Example.
• Bumped the schema-reference version note v0.14.0 -> v0.19.0 (the release that ships these fields, so the page no longer documents a field that predates its own version marker).

Checks: bun run lint:md, bun run format:check, and bun run build all pass.

No observability.md change - that page covers the gateway's env-var telemetry, a separate surface from the ADL manifest field. No follow-up tickets: docs-only change to an already-merged schema, authored in the docs repo itself.

PR: #399

• branch docs/issue-397-20260715-0106