Support service account tokens

[vijaybandari]

Current sdk sets the token header as Apikey.

with httpx.Client(
    headers={
        "Authorization": f"ApiKey {self.access_token}",
        "Accept": "application/json",
    },
    timeout=self.timeout
) 

But the lightdash api expects the service account tokens to be prefixed with Bearer

// If it is not a specific Bearer token, we do next, without throwing an error
// This could be an ApiKey token, or already authenticated user
if (tokenParts.length !== 2 || tokenParts[0] !== 'Bearer') {
    // We will execute the next middleware
    next();
    return;
}

[linear]

PROD-7069