Provide a complete documentation page for the webclient network utility
in Documentation/applications/netutils/webclient/index.rst, replacing
the previous 7-line placeholder stub.
Includes:
- Architecture overview (NSH wget engine + programmatic C API)
- Key features (HTTP/1.0, HTTP/1.1, chunked encoding, pluggable TLS,
non-blocking I/O, proxy tunneling)
- Detailed Kconfig configuration table and dependencies
- NSH wget syntax, options, and real-world usage examples
- C API reference for simple helpers (wget, wget_post) and the
context-based API (struct webclient_context)
- Complete, runnable C application example for file downloads
Addresses #11081
Signed-off-by: Swatantra Yadav <maverickswatantra@gmail.com>
