Provide context of last relay switch

[mcspr]

ref #1264

What about having relay_t struct extended with module-specific enum, e.g

enum class SwitchContext {
#if TERMINAL_SUPPORT
    TERMINAL,
#endif
#if BUTTON_SUPPORT
    BUTTON,
#endif
#if DOMOTICZ_SUPPORT
    DOMOTICZ,
#endif
#if THINGSPEAK_SUPPORT
    THINGSPEAK,
#endif
#if MQTT_SUPPORT
    MQTT,
#endif
    NONE
};

Plus, additional option to ignore same context when it is the source of the switch.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[mcspr]

Going with slightly different approach (not hardcoding all possible sources), so might as well close this.