Add dashboard observability for raio shards

[rozbb]

Question: One thing I'm not clear on is where the observability key is supposed to go in wrangler.jsonc. Can it be scoped to environment or does it need to be global?

[fisherdarling]

The key can be scoped to both an environment and globally as well. Take a look at https://developers.cloudflare.com/workers/observability/logs/workers-logs/#enabling-with-environments

Also, we might as well enable workers tracing too: https://developers.cloudflare.com/workers/observability/traces/#how-to-enable-tracing
that'll help us find any deeper causes of latency. I think the RPS rate can be high (?) so 5% sampling like in the docs seems fine to me.