[FEATURE REQ] Update quick-start doc of Spring Kafka to include credential-free connection

[saragluna]

Context

We already shipped the quickstart doc of Kafka using credential-free connection, but we need to modify it according to the new template.

There's a template worked out by Alex can be found here:

• https://github.com/MicrosoftDocs/azure-docs-pr/pull/203348#issuecomment-1205727432
• https://github.com/MicrosoftDocs/azure-docs-pr/pull/203348#issuecomment-1203381358

We should demo two connection methods in this doc, one using credential-free connections and one using username/password, using contextual tabs to distinguish them. We should make the credential-free tab as the default/recommended.

Goal

Update the quick-start doc to include the credential-free part.