Authentication with additional_headers is not possible

[dennis-ge]

Bug Description

When creating a new client, setting the Authorization header via the additional_headers parameter is not working:

weviate_client = client.Client(
        url="http://localhost:8080",
        additional_headers={"Authorization:": "Bearer xyz"},
    )

The following error is thrown:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../venv/lib/python3.10/site-packages/weaviate/client.py", line 146, in __init__
    self._connection = Connection(
  File ".../venv/lib/python3.10/site-packages/weaviate/connect/connection.py", line 580, in __init__
    super().__init__(
  File ".../venv/lib/python3.10/site-packages/weaviate/connect/connection.py", line 117, in __init__
    self._create_session(auth_client_secret)
  File ".../venv/lib/python3.10/site-packages/weaviate/connect/connection.py", line 180, in _create_session
    raise AuthenticationFailedException(msg)
weaviate.exceptions.AuthenticationFailedException: "No login credentials provided. The weaviate instance at http://localhost:8080 requires login credentials.

                    Please check our documentation at https://weaviate.io/developers/weaviate/client-libraries/python#authentication
                    for more information about how to use authentication.

This error is thrown in the _create_session method because the used weviate instance has an OIDC configuration but no auth_client_secret was provided.

I also saw that a previous issue (#177) already adressed this, but the proposed solution didn't fix it.

Proposed Solution

The case when an Authorization header is present in the additional_headers dict can be handled in the same way as the newly introduced AuthApiKey at the top of the _create_session. If the header is present in the private _headers dict of the BaseConnection, a new session can be created and the method can be exited.

I can also provide a PR if wanted.

[dirkkul]

I can also provide a PR if wanted.

That would be great, your proposed solutions sounds good. Please with a test in this file :)