refactor(unstable): otel configuration (#27333)
split up otel config into user configurable and runtime configurable
parts. user configurable part is now set via env vars parsed according
to the otel spec. otel is now enabled via `OTEL_DENO=true`, and
`--unstable-otel` only acts as a guard.
Fixes: https://github.com/denoland/deno/issues/27273
