Added code to force authentication on first request instead of authentication-challenge

[enothen]

Added "forceauth" parameter to address issue #175.

Current default behavior is kept:

>>> h = httplib2.Http(".cache")
>>> h.add_credentials(user, password)
>>> headersDict={'Content-Type':'application/json','accept':'application/json'}
>>> response, content = h.request(url, 'GET', headers=headersDict)
>>> 
>>> response.status
401
>>> 

The webserver in the example above does not return a "www-authenticate" header, and so authentication is not tried (even though credentials are provided and a 401 is received in the first attempt):

>>> response
{'date': 'Wed, 31 May 2023 12:29:44 GMT', 'server': 'Apache', 'content-type': 'application/json; charset=utf-8', 'apipie-checksum': '5346b3362dcb7d38bd1dd226bc763427f7fe8200', 'cache-control': 'no-cache', 'x-request-id': 'e27cfd25-00ad-466a-b03f-c1a849001697', 'x-runtime': '0.026089', 'strict-transport-security': 'max-age=631139040; includeSubdomains', 'x-frame-options': 'sameorigin', 'x-content-type-options': 'nosniff', 'x-xss-protection': '1; mode=block', 'x-download-options': 'noopen', 'x-permitted-cross-domain-policies': 'none', 'content-security-policy': "default-src 'self'; child-src 'self'; connect-src 'self' ws: wss:; img-src 'self' data:; script-src 'unsafe-eval' 'unsafe-inline' 'self'; style-src 'unsafe-inline' 'self'", 'via': '1.1 satellite.keller.lab', 'transfer-encoding': 'chunked', 'status': '401'}

And from the webserver side:

192.168.122.149 - - [31/May/2023:12:29:44 +0000] "GET /api/hosts HTTP/1.1" 401 58 "-" "Python-httplib2/0.13.1 (gzip)"

Forcing auth allows successful login on the first try:

>>> h2 = httplib2.Http(forceauth="basic")
>>> h2.add_credentials(user, password)
>>> response, content = h2.request(url, 'GET', headers=headersDict)
>>> 
>>> response.status
200
>>> 

192.168.122.149 - - [31/May/2023:12:45:05 +0000] "GET /api/hosts HTTP/1.1" 200 69189 "-" "Python-httplib2/0.13.1 (gzip)"

Feedback/corrections are welcome, as this is my first take of an issue here in httplib2.