Doc: provide more details and examples to each auth provider

[binbin-li]

What would you like to be added?

Ratify supports 5 auth providers which are listed in the doc. And each provider has its own configuration to be set. But the doc doesn't provide detailed parameters for each provider and miss samples for some providers. We need to improve the doc to bridge the knowledge gap.

Anything else you would like to add?

No response

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.

[yizha1]

Missing doc for "Azure Managed Identity" based on discussion on 8/29/2023.