feat: added some useful http headers to context

[peppelinux]

This PR adds in satosa context object some useful HTTP request headers in a private attribute called _http_headers. these are the following

• REQUEST_METHOD
• PATH_INFO
• REQUEST_URI
• QUERY_STRING
• SERVER_NAME
• REMOTE_ADDR
• HTTP_HOST
• HTTP_USER_AGENT
• HTTP_ACCEPT_LANGUAGE

With these additional values we would allow some highly specialized feature in the future Microservices. Some example:

• Security: SIEM integrations, checks upon SERVER_NAME, QUERY_STRING, HTTP_USER_AGENT
• i18n: HTTP_ACCEPT_LANGUAGE

All Submissions:

• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Have you added an explanation of what problem you are trying to solve with this PR?
• [x] Have you added information on what your changes do and why you chose this as your solution?
• [ ] Have you written new tests for your changes?
• [x] Does your submission pass tests?
• [x] This project follows PEP8 style guide. Have you run your code against the 'flake8' linter?

[c00kiemon5ter]

@peppelinux we will be merging this PR.

I think the extracted headers could also be configurable. We will re-iterate to do this and probably handle it outside of the proxy-application but as its own middleware.

[peppelinux]

@peppelinux we will be merging this PR.

I think the extracted headers could also be configurable. We will re-iterate to do this and probably handle it outside of the proxy-application but as its own middleware.

seems quite resonable to me, thank you