Refactor connect to use libcurl instead of cpprestsdk/curl

Starting form 10.2.37 Connect SE is using curl, introduced by Olivier Bertrand, commit 8c617e99015c.

cpprestsdk that has to be build by user, can be removed and use libcurl, so remove cppreset and optimize code for libcurl only by covering REST with test cases.
The task should consists of:
1. Drop all restcppsdk references
2. Drop all exec(curl) references.
3. Link to libcurl (both on Linux and on Windows).
4. Use libcurl api to issue HTTP requests.
5. Buildbot (bb) CI was never tested on Windows with cpprestsdk. Allow test on Windows on bb with libcurl.
6. Make sure that this patch covers also update in documentation pages:
[1] https://mariadb.com/kb/en/connect-files-retrieved-using-rest-queries/
[2] https://mariadb.com/kb/en/connect-making-the-getrest-library/ [deprecate]