python-tackerclient drop content-type when using HTTPClient

[Ayumu Ueha]

If the `_cs_request()` method called by `do_request()` of HTTPClient class (in python-tackerclient code) [1] contains `content-type` in `kwargs`, an error occurs if `content-type` is not `application/json` because `content-type` has not copied to the kargs passed to request.

[1] https://opendev.org/openstack/python-tackerclient/src/branch/stable/2023.2/tackerclient/client.py#L83-L98

```
    L83~

    def _cs_request(self, *args, **kwargs):
        kargs = {}
        kargs.setdefault('headers', kwargs.get('headers', {}))
        kargs['headers']['User-Agent'] = self.USER_AGENT

        if 'body' in kwargs:
            kargs['body'] = kwargs['body']

        *** Not dealing with `content-type` in kwargs ***

        if self.log_credentials:
            log_kargs = kargs
        else:
            log_kargs = self._strip_credentials(kargs)

        utils.http_log_req(_logger, args, log_kargs)
        try:
            resp, body = self.request(*args, **kargs)
        ...(omit)...
```