Set an app's server monitoring

Turns OpenTelemetry tracing on or off for the app. `manual` and `auto` add the app variables OTEL_EXPORTER_OTLP_ENDPOINT, OTEL_EXPORTER_OTLP_PROTOCOL, OTEL_EXPORTER_OTLP_COMPRESSION, OTEL_RESOURCE_ATTRIBUTES, OTEL_METRICS_EXPORTER and OTEL_LOGS_EXPORTER, which point an OpenTelemetry SDK at Cloady's trace store, and each service also gets OTEL_SERVICE_NAME. `auto` also writes CLOADY_SERVER_MONITORING, the agent for each service (`web=node,worker=python`), and Cloady loads that OpenTelemetry agent into the service when it starts, with no code change. `agents` sets the agent of each service it names, null removing it, and the other services keep the agents CLOADY_SERVER_MONITORING already lists (none unless the app is already in `auto` mode); without `agents` Cloady detects what each service runs and picks every agent itself. `off` deletes them all. The app is reconciled: turning it on or off restarts its running services once, and changing agents restarts only the services whose agent changed; a request that changes nothing restarts nothing. Answers 400 for a service the app doesn't have, and 502 when the variables were saved but the app couldn't be reconciled, which repeating a `manual` or `auto` request retries. Needs the developer role.

curl -X PUT "https://example.com/api/workspaces/string/apps/string/tracing" \  -H "Content-Type: application/json" \  -d '{    "mode": "off"  }'

{  "mode": "off",  "services": [    {      "name": "string",      "env": {        "property1": "string",        "property2": "string"      },      "receiving": true,      "agent": "node",      "start": {        "property1": "string",        "property2": "string"      }    }  ]}