fix: firebase documentation after 0.9 upgrade

[xavidop]

This PR updates the docs after upgrading to 0.9.0:

1. Since the firebase emulator and the genkit UI uses by default the same port (4000), it is better to start first the genkit UI and then the firebase emulator. The firebase emulator autodetect that the port 4000 is in use and uses another one.
2. Added the npm command provided by the firebase template npm run genkit:start
3. fixes this visualization problem: https://firebase.google.com/docs/genkit/monitoring#trace_storage_and_developer_ui

Checklist (if applicable):

• Tested (manually, unit tested, etc.)
• Changelog updated
• Docs updated

[MichaelDoyle]

@xavidop this is awesome. would you mind splitting the code changes from the docs changes (i.e. 2 PRs), since they are not related? I think we'll have an easier time getting the right folks to review that way.

Mike D

[xavidop]

@xavidop this is awesome. would you mind splitting the code changes from the docs changes (i.e. 2 PRs), since they are not related? I think we'll have an easier time getting the right folks to review that way.

Mike D

@MichaelDoyle done!