Add CPU temp sensor path selection option

[N7-BADA]

Closes #7870

Adds option to manually select CPU temperature sensor path.

Changes:

• dietpi.txt: new SOFTWARE_DIETPI_CPU_TEMP_PATH setting
• dietpi-globals: check for user-defined path before auto-detection
• dietpi-config: menu option under Display Options to select sensor from available sysfs nodes

Users can pick from detected sensors, enter a custom path, or keep auto-detect.

[nonnorm]

Note for myself: read through this PR later and see if it could be applied to make dashboard temp sensing more accurate.

[N7-BADA]

Applied both suggestions, renamed the setting from SOFTWARE_DIETPI_CPU_TEMP_PATH to CONFIG_CPU_TEMP_PATH
Switched default handling to explicit CONFIG_CPU_TEMP_PATH=auto
Updated dietpi-globals to use:

: "${G_HW_CPU_TEMP_PATH:=$(sed -n 's/^CONFIG_CPU_TEMP_PATH=//p' /boot/dietpi.txt)}"
[[ $G_HW_CPU_TEMP_PATH == 'auto' ]] && G_HW_CPU_TEMP_PATH=

Updated dietpi-config accordingly to use CONFIG_CPU_TEMP_PATH
Simplified the menu handler so all selection paths end in a single:

G_CONFIG_INJECT 'CONFIG_CPU_TEMP_PATH=' "CONFIG_CPU_TEMP_PATH=$G_WHIP_RETURNED_VALUE" /boot/dietpi.txt

Tested again with new changes and still works.

[MichaIng]

I moved the menu to performance options and simplified it by using the sensor paths as menu index. Also added the coretemp API. But those paths can be long, let's see whether it looks fine, else we could implement some mechanism to only show the last X characters in the menu, prefixed with ... or so.

The display options are meant to be about video output and camera features. The benefit about performance options is that it already shows the temperature above the menu. So one can see the effect immediately, and if spottet false temperature there the right option is right below.

[MichaIng]

Works great. On narrow screens it might look weird, but otherwise the max menu width of 120 characters has more than enough space.