feat(wlan): Implement additional wlan operation modes (access point, disabled)

[Slider0007]

1. Implement additional wlan operation modes (beside default WLAN client mode)

• Access point mode for standalone operation (full WebUI functionality)
  • Add a optional timed-off option to suspend WLAN connection after a configurable time is elapsed, no client is connected and actual cycle processing is completed.
• WLAN client mode (default access mode, already exisiting):
  • Add a optional timed-off option to suspend WLAN connection after a configurable time is elapsed and actual cycle processing is completed.
  • Add a fallback to access point operation mode if network connection cannnot be established initially after > 120s (chnaged from retries to time in (wlan): Use time delay instead of retires to determine fallback AP start #190) (e.g. wrong password) --> Access point is automatically activated to be able to connect via device's access point again and interact with the device
• WLAN disabled (no interaction possible, but device is able to process and log data to SD card)

2. Add GPIO pin mode to resume a suspended WLAN connection by a GPIO pin defined in GPIO section.

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Further changes:

• Code: Refactor variable / function naming + harmonization of wlan and mqtt interface
• WebUI: Indicate and perform a required reboot for changing hardware related parameter (Button label: Save And Reboot). For all other parameter still no reboot is required (Button label: Save And Apply).

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Usage before (based on ESP32):
RAM: [= ] 14.1% (used 46096 bytes from 327680 bytes)
Flash: [========= ] 87.0% (used 1692537 bytes from 1945600 bytes)

Usage after:
RAM: [= ] 14.1% (used 46272 bytes from 327680 bytes)
Flash: [========= ] 87.3% (used 1697765 bytes from 1945600 bytes)