Add an Alloy-based collector config as an alternative to the reference
OpenTelemetry Collector. It forwards xrpld OTLP traces and native metrics
to the Grafana Cloud OTLP gateway and, critically, runs a spanmetrics
connector so span-derived RED metrics (span_calls_total,
span_duration_milliseconds_*) are produced. Those metrics are not emitted
by xrpld; they are derived from spans, so an Alloy node without this
connector is missing from every span-based dashboard.
All credentials, endpoints, usernames and the per-node host label are read
from the environment (no secrets in the file). Adds a matching
.env.grafanacloud-alloy.example and gitignore exception, and the otelcol
term to the cspell dictionary.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
