feat(js/plugins/compat-oai): allow passing api key at runtime instead of config time

[pavelgj]

const ai = genkit({
  plugins: [openAI({apiKey: false})],
});


await ai.generate({
  prompt: 'tell me why...',
  model: openAI.model('gpt-4o'),
  config: {
    apiKey: '...'
  }
});

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[ssbushi]

What is the point of supporting per-request API keys?

[pavelgj]

What is the point of supporting per-request API keys?

Folks build apps where user provides the API key. The key is dynamically fetched from a DB.

[ssbushi]

LGTM, save for 1 small comment.