Add logLevel and logTimestamps options to vpnc-script-win.js

Add logLevel and logTimestamps options to vpnc-script-win.js

Based on discussions about how to improve vpnc-script logging in
https://gitlab.com/openconnect/vpnc-scripts/-/issues/32#note_810779624.

See https://gitlab.com/openconnect/openconnect/-/merge_requests/328,
which makes OpenConnect send its verbosity level to the vpnc-script
as $LOG_LEVEL.

In the future, $LOG_TIMESTAMPS should probably also be passed by
OpenConnect, although this may be unnecessary since most OS's logging
systems can add timestamps on their own.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>