Missing `--app-config` option

[LDong-Arm]

Describe the bug
Mbed CLI 1 offers an --app-config option to let users specify the application configuration JSON instead of assuming mbed_app.json. This is not currently provided by mbed-tools, but useful when

• one application provides multiple configurations for different use cases
• different applications or tests share one common configuration (e.g. experimental.json)

To Reproduce
Try to build an application (e.g. blinky) with --app-config, for example

mbed-tools compile -t GCC_ARM -m K64F --app-config mbed-os/TESTS/configs/experimental.json

and the error is

Error: no such option: --app-config

Expected behavior
An option --app-config is available to both mbed-tools configure and mbed-tools compile. The specified JSON is used for generating mbed_config.cmake.

Screenshots
N/A

Desktop (please complete the following information):

• OS: Any
• Version: Any

Mbed (please complete the following information):

• Device: Any
• Mbed OS Version: 6.11.0
• Mbed CLI 2 Version: 7.23.0

Additional context
N/A