samples: http_get: add tests with Native Simulator offloaded sockets

'http_get' is one of the few samples that just require connection to
internet (google.com over HTTP or HTTPS) and check if HTTP GET was
successful. Use it for minimal coverage of Native Simulator offloaded
sockets:

 * DNS resolving
 * basic TCP transfer
 * compatibility with Zephyr TLS subsystem (which required some fcntl()
   operations)

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>