Oidc Access Token Provider

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I have now implemented quite a few times `OidcTokenAccessProvider`, for example [here](https://github.com/redhat-developer/kiota-java-extra/blob/main/rh-auth/src/main/java/com/redhat/cloud/kiota/auth/RHAccessTokenProvider.java).

Despite it being almost trivial in the end user codebase it turns out that is difficult to refactor the mechanism up to this repository.
More specifically the challenges are:

- Access to an `HttpClient` (or `RequestAdapter` but I think there are a few gaps later on) - possibly we should be able to decide to use the same or a different one from the "normal" API calls
- encode a form body is pretty straightforward with a bare HTTP client, not sure how that looks like with bare Kiota without the generated classes
- decode a Json response
- etc...

I'm here looking for guidance on how we can approach the problem.
I have attempted at first to add an `initialize` method to `AccessTokenProvider` and to `AuthenticationProvider` so that it can be eventually triggered by the `RequestAdapter` implementation.
I started having too many things to pull in and thought that it was not a great design ...

Inizia leggendo le interfacce AccessTokenProvider, AuthenticationProvider e RequestAdapter, quindi confronta l’implementazione RHAccessTokenProvider indicata. Chiarisci come devono essere esposti l’accesso HTTP, la codifica dei form e la decodifica JSON senza classi generate; l’issue sarà pronta solo dopo aver concordato il design dell’API e il percorso di integrazione previsto.

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