[FEATURE REQ] Support for Credentials and Credentials Manager

### Please describe the feature.

Currently, we can use [credential manager](https://learn.microsoft.com/en-us/azure/api-management/credentials-overview) to configure and manage connections (formerly called authorizations) for backend OAuth 2.0 APIs.

It could be great to have this support in apiops

There might be some challenges on handling secrets(client secrets) to be passed as till now there is no native support for keyvault to fetch the secret directly into credentials manager. But as a suggestion we can look into environment variables instead of putting into yaml/source control