Respect log levels

[ssbushi]

Note: The CLI is not affected by this change.

[ssbushi]

Output on genkit flow:run jokeFlow if logging level is set to error:

Starting app at `lib/index.js`...
Warn: Port 3100 not available, using 3101 instead.
Reflection API running on http://localhost:3101
Running '/flow/jokeFlowSimple' (stream=false)...
Flow operation:
{
  "name": "c9f494b8-0cb7-44dc-98e4-564b37d38da1",
  "done": true,
  "result": {
    "response": "What do you call a banana that's been in the sun too long?\n\nA banana split."
  }
}
App process exited with code 0