This uses the opentelemetry SDK to provide support for traces and two
simple metrics (a conversations count and a messages count).

The telemetry entrypoint is built separately (unfortunately it does not
seem like there is a method for doing this in one build as sveltekit
overrides rollupOptions).

As written the metrics may be too high cardinality for some use cases
(as they are keyed per user), but these attributes can always be dropped
in a collector.

Resolves the issue described in open-telemetry/opentelemetry-js#3944

As written these were always undefined, can re-add them later if
desired.