Suppress the OTel SDK's auto-configured exporters

With the metrics and logs SDK gems loaded, `OpenTelemetry::SDK.configure`
auto-installs a metrics reader and a log processor based on the
OTEL_METRICS_EXPORTER / OTEL_LOGS_EXPORTER env vars, which default to
"otlp" pointed at the default OTLP endpoint. Each spawns a background
thread. Collector mode replaces both providers with its own right
after, orphaning those threads where no shutdown can reach them.

Default the env vars to "none" so the SDK skips the auto-setup; the
exporters collector mode builds explicitly are the only ones that
should run. User-set values still win.

[skip changeset]

Author: unflxw

lib/appsignal/opentelemetry.rb

@@ -24,6 +24,16 @@ def configure(config)
         # this preference, per the OTel spec.)
         ENV["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"] ||= "delta"
 
+        # With the metrics and logs SDK gems loaded, `SDK.configure` below
+        # auto-installs a metrics reader and a log processor from these env
+        # vars (both default to "otlp", pointed at the default OTLP
+        # endpoint), each with its own background thread. We replace both
+        # providers with our own right after, which would orphan those
+        # threads -- unreachable by any shutdown. Suppress the auto-setup;
+        # the exporters we build below are the only ones that should run.
+        ENV["OTEL_METRICS_EXPORTER"] ||= "none"
+        ENV["OTEL_LOGS_EXPORTER"] ||= "none"
+
         require "opentelemetry/sdk"
         require "opentelemetry/exporter/otlp"
         require "opentelemetry-metrics-sdk"