Implementation of the option http.header2cgi

[ffurano]

No description provided.

[ffurano]

After merging the pull request, the docs should be added an additional paragraph containing something like the following:

---

6.3.7 header2cgi
http.header2cgi <headerkey> <CGIkey>

Function:
When a request comes, pick the value associated to the HTTP header <headerkey> (if present) and append it to the CGI information of the path that xrootd will process internally, in the form "<CGIkey>=<value>"

Parameters:
headerkey: the header key that is looked for
CGIkey: the CGI key that will be appended to the internal CGI information

Defaults:
none

Notes:

1. <headerkey> and <CGIkey> can be equal

Example:
http.header2cgi Authorization authz