make flows optional on ai.startFlowServer

[zerolethanh]

Is your feature request related to a problem? Please describe.
I have to import many flows when run ai.startFlowServer

Describe the solution you'd like
public this registeredFlows prop? or something like optional flows prop on ai.startFlowServer, e.g: ai.startFlowServer({flows?:[...ai.registeredFlows]})

Describe alternatives you've considered
We have designed flows system by read flows.ts|.js in sub-folders like:

/src | /lib
  '- /flows/
       '- /users/
          '- flows.ts|.js <-- at this point `export {userListFlow} from './list/userListFlow'`
          '- /list/
              '- userListFlow.ts|.js

/// read flows code
const allFlowsDir = path.resolve(devEnv ? "src" : "lib", "flows");
fs.readdirSync(allFlowsDir).forEach((name) => {
    const flowDir = path.join(allFlowsDir, name);
    logInfo("loading flow:", flowDir);
    try {
        require(path.join(flowDir, "flows")); // require flows.ts|.js
        logSuccess(`loaded flow: ${flowDir}`);
    } catch (e:any) {
        console.log((e as Error).stack)
    }
});

Additional context

[zerolethanh]

currently, we resolved this issue by this solution:

// read all flows in /flows dir
const allFlowsDir = path.resolve(devEnv ? "src" : "lib", "flows");
type IFlows = FlowServerOptions['flows']
const allFlows: IFlows = []

fs.readdirSync(allFlowsDir).forEach((name) => {
    const flowDir = path.join(allFlowsDir, name);
    // logInfo("loading flow:", flowDir);
    try {
        const flowList = require(path.join(flowDir, "flows")); // require flows.ts|.js
        if (flowList) {
            const flows = Object.values(flowList) as IFlows
            allFlows.push(...flows)
        }
        // logSuccess(`loaded flow: ${flowDir}`);
    } catch (e: any) {
        logError(e);
    }
});

ai.startFlowServer(
  {
    flows: allFlows
  }
);

[apascal07]

@pavelgj Exposing Genkit.registeredFlows seems reasonable even if we were to deprecate/not recommend Genkit.startFlowServer anymore since users may still want to iterate through all of them to add to their own server.

Thanks for the suggestion, @zerolethanh!