Migrate READMEs to new Genkit Release

[MaxHamscher]

Issue
The READMEs (e.g. genkitx-azure-openai) state outdated genkit setups depending for instance on configureGenkit instead of genkit for initializing.

Possible Solutions
Migrate the READMEs carefully to the release, e.g. with

import { genkit } from 'genkit';

and

export default genkit({ plugins: [ azureOpenAI({...}), ], });

Additional context
See in particular the official migration guide: https://firebase.google.com/docs/genkit/migrating-from-0.5