net/http: Add the HTTP/1.1 API

This patch adds the HTTP/1.1 API for Zephyr. This API consists of client
and server context structures enabled via Kconfig variables.
HTTP parser support is enabled via the CONFIG_HTTP_PARSER configuration
variable.

Currently, this API only includes support for writing HTTP requests
(client mode) and HTTP responses (server mode). TLS support is not
considered in this iteration.

Supported HTTP methods:
	GET, HEAD, OPTIONS and POST.

Supported HTTP responses:
	400, 403 404. The http_response routine may be used to write
	any HTTP status code, for example 200 OK.

Jira: ZEP-1701

Change-Id: Ic9ccd4d4578d6d0f3a439976ea332b031644ca7d
Signed-off-by: Flavio Santes <flavio.santes@intel.com>