feat: align tracing exporters with OTLP

[casey-quinn]

Summary

• pivot tracing configuration to new shared exporter field with OTLP HTTP defaults and env fallbacks
• update all service defaults/revaconfig wiring to surface exporter while keeping legacy knobs gated
• prune jaeger vendor tree and add otlp-http/stdout exporters plus tracetest helpers

Refs #1906

Testing

• nix shell nixpkgs#go nixpkgs#libxcrypt --command bash -lc 'export CPATH=$(nix eval --raw nixpkgs#libxcrypt)/include; export LIBRARY_PATH=$(nix eval --raw nixpkgs#libxcrypt)/lib; go test ./...'
• nix shell nixpkgs#go nixpkgs#libxcrypt --command bash -lc 'export CPATH=$(nix eval --raw nixpkgs#libxcrypt)/include; export LIBRARY_PATH=$(nix eval --raw nixpkgs#libxcrypt)/lib; make golangci-lint'

[rowan-stein]

Per maintainer guidance (https://github.com/opencloud-eu/opencloud/pull/1910#issuecomment-3576508667), this PR collapses tracing to a single exporter selector: , , or , and uses standard OTEL env vars for OTLP configuration. Paired PR in reva: https://github.com/opencloud-eu/reva/pull/436.\n\nIf acceptable, please add a label (e.g., ) so the label workflow can pass. Happy to iterate on naming/defaults if you prefer different defaults (e.g., default exporter).

[rowan-stein]

Gentle reminder: please add a label (e.g., ) so the label workflow can pass. CI is running (Woodpecker checks pending). We’ll iterate quickly on any feedback.