[REQ][rust] Readuce `bearer_access_token` and `oauth_access_token` to `access_token`

Is your feature request related to a problem? Please describe.

There is no difference in bearer_access_token and oauth_access_token to access_token in generated Configuration (and also in bearer_auth cases called bearer_auth)

Describe the solution you'd like

Replace:

#[derive(Debug, Clone)]
pub struct Configuration {
...
    pub oauth_access_token: Option<String>,
    pub bearer_access_token: Option<String>,
....
}

with:

#[derive(Debug, Clone)]
pub struct Configuration {
...
    pub access_token: Option<String>,
....
}

And in client implementation put only one auth header (even if multiple auth schemes provided) for both hyper and reqwest implementation.

Caution! It may break usage of already generated code.

Start by locating the generated Rust Configuration and client implementation for both hyper and reqwest, then compare how bearer_auth and the two access-token fields are handled. Done means both implementations use access_token and emit only one auth header, with compatibility impact considered.