Add a "curl" configuration for the linum-stm32h753bi board, based on the
netnsh configuration (ethernet + DHCP). It enables the system/curl HTTP
client command, SD card support (mounted manually, as in the sdcard
configuration) and a larger console line buffer (CONFIG_LINE_MAX=256) so
long URLs and JSON bodies are not truncated at the NSH prompt.
Also document the curl command: add a man page under
Documentation/applications/system/curl and a usage example (download,
POST JSON, multipart upload) to the board documentation.
Signed-off-by: Jorge Guzman <jorge.gzm@gmail.com>