Allow user to pass headers to jikan requests

[purarue]

As stated in #54, adding header support would be good to allow users to bypass caching, and compare ETag values

Current thoughts/issues:

• I believe, coincidentally, the way I laid out _wrap_response already works for ETag checking (304s). It defaults to {}, does nothing in except block and, doesnt get modified in _check_response, and then has the headers/url added to it. So the 304 would just return a dict with the jikan_url and response headers (which I think is what we want).

json_response: Dict = {}
try:
    json_response = response.json()
except json.decoder.JSONDecodeError:
    # json failed to be parsed
    # this could happen, for example, when someone has been IP banned
    # and it returns the typical nginx 403 forbidden page
    pass
self._check_response(response_dict=json_response, response_status_code=response.status_code, **kwargs)
return self._add_jikan_metadata(response, json_response, url)

• Add default_headers to abstractjikan? That way if someone wants to set a User-Agent to identify themselves to api.jikan.moe. Then headers passed per request can override with dict.update

Not totally sure how to implement a 304 pytest, but I'll give it a try.

No Estimate currently on when I'll have this done.

[irfan-dahir]

304 can be tested in the following way

1. Get value ETag from a request.
2. Next time that request is made, pass an If-None-Match header with the ETag value as it's value.
3. If data is unchanged, response code will be 304 - Not Modified. The standard output for 304 is empty body. So only a header check for 304 is required to determine that the data is unchanged.
   If data has changed; response will be how it usually is. 200 - OK with the response (updated/changed data) in the body.

Better explained with a diagram: https://jikan.docs.apiary.io/#introduction/cache-validation

[purarue]

As per the discussion in discord:

• Allow users to override session objects, document how to set default headers for jikan/aiojikan
• Let users pass additional kwargs which get passed to session.get

For jikan:

https://2.python-requests.org/en/master/api/#requests.request

Accept a subset of the kwargs that are relevant (to avoid confusion with params/parameters):

headers
cookies
timeout
allow_redirects
proxies
verify
stream
cert

The other ones we can ignore since we're the ones creating data for them:
url
method
params (get fields)

Or theyre just not relevant:

data (for post requests)
json (for post requests)
files

Similarly, accept a subset of kwargs from aiohttp.Session.get

https://aiohttp.readthedocs.io/en/stable/client_reference.html#aiohttp.ClientSession.request

Document which kwargs are allows to be passed.

Add a function: _check_request that gets called before the request is sent, that checks (jikan/aiojikan specific) if the kwargs are allowed (by defining a list of them in parameters.py)

[purarue]

Could probably just wait till v4 since some subset of the API will have to be rewritten to handle passing the JWT, and the parameter checks are being removed anyways.