Build fail when passing CONFIG_ string assignment from the command line

[fabiobaltieri]

Describe the bug
Hey folks, looks like passing string configs from the command line broke with #85994

$ west build -p -b nrf52dk/nrf52832 samples/hello_world/ -DCONFIG_BOOT_BANNER_STRING=\"broken\"
...
CMake Error at /home/fabiobaltieri/zephyrproject/zephyr/cmake/modules/yaml.cmake:552 (string):
  string sub-command JSON failed parsing json string: * Line 81, Column 134

    Missing ',' or '}' in object declaration

  .

added a print for ${json} to figure what's going on and this is the problematic line:

    "command" : "/home/fabiobaltieri/.venv/bin/west build -p -b nrf52dk/nrf52832 samples/hello_world/ -DCONFIG_BOOT_BANNER_STRING=\\"broken\\"",

usual multiple escape issue it seems.

@tejlmand @pillo79 @nordicjm could any of you folks look into it?

Thanks!

To Reproduce
See above

Expected behavior
Build happily

Impact
It's pretty bad

Environment (please complete the following information):
v4.1.0-rc2, Zephyr SDK, Linux, the usual

[fabiobaltieri]

cc @kartben

[kartben]

#86151 reports a similar issue

[noahp]

Also impacting our CI, we've reverted for now.