Add initial version of script for enabling and disabling console in FNGS

This is a part of the fix for issue [746-000797] Flash-N-Go System: Implement "Disable serial console"

The script is intended to enable and disable console in fngsystem:

• when the script is ran with --disable-console argument, a boot-alt.cfg will be adjusted to remove "console" argument from kernel command line;
• and when this script is ran with --enable-console argument, the console will be enabled again.

Example: sh /usr/share/yocto-install/fngsystem-console-update.sh --disable-console

Two other related MRs:

• seco-ne/yocto/layers/meta-seconorth-distro!719 (merged)
• seco-ne/yocto/layers/meta-seconorth-machine!514 (closed)