feat: add otelsetup subpackage for shared OTEL provider init

Extracts the OpenTelemetry provider initialisation logic from
kubescape/node-agent into a reusable go-logger/otelsetup package so
any kubescape service can get OTLP gRPC provider setup, ARMO auth
header injection, per-signal exporter gating, TLS/plaintext detection,
and the retroactive ring-buffer log processor without copy-pasting
boilerplate.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>