Play Framework

feat: OTLP push exporter for metrics via micrometer-registry-otlp (PF-82)

Layers an optional OtlpMeterRegistry alongside the existing Prometheus
pull endpoint introduced in PF-13. When metrics.otlp.endpoint is set,
MetricsPlugin wraps both registries in a CompositeMeterRegistry and
installs the composite via Metrics.install(). Custom meters and JVM
binders register on the composite once and propagate to both backends;
the /@metrics scrape continues to read from the Prometheus registry
directly. When the endpoint is unset, behavior is unchanged from PF-13:
the Prometheus registry is installed standalone.

Configuration keys (all under metrics.otlp.*):
- endpoint: empty disables OTLP; otherwise the OTLP/HTTP collector URL
- step: push interval; accepts 60s/1m/PT60S short forms with a 60s
  fallback on parse failure
- headers: K=V,K=V list of HTTP headers (auth, routing)
- resourceAttributes: K=V,K=V OTLP resource attributes

Adds micrometer-registry-otlp 1.13.6 plus its required runtime
transitives (opentelemetry-proto 1.2.0-alpha, protobuf-java 3.23.4).
The Prometheus side already ships its own shaded protobuf, so the
unshaded one declared here is OTLP-only and cannot collide.

Tests in MetricsPluginOtlpTest cover: endpoint-empty stays
Prometheus-only, endpoint-set installs a composite with both
registries, custom meters reach both backends, KV-list parsing for
headers and resource attributes, short-form and malformed step
parsing, and onApplicationStop closes both component registries.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>