Add a multi channel example

Added a multi channel example with run limit, tilting and channel selection
features. Refs #1104 and closes #1111.

examples/relay_chn_multi/main/Kconfig.projbuild

@@ -0,0 +1,52 @@
+menu "Relay Channel Multi Example Configuration"
+    
+    choice EXAMPLE_RLCHN_BTN_ACTIVE_LEVEL
+        prompt "Choose an active level for buttons"
+        default EXAMPLE_RLCHN_BTN_ACTIVE_LEVEL_LOW
+        help
+            Specify the active level for buttons.
+        
+        config EXAMPLE_RLCHN_BTN_ACTIVE_LEVEL_LOW
+            bool "Active level LOW"
+
+        config EXAMPLE_RLCHN_BTN_ACTIVE_LEVEL_HIGH
+            bool "Active level HIGH"
+    endchoice
+    
+    config EXAMPLE_RLCHN_BTN_UP_IO_NUM
+        int "GPIO number for UP button"
+        default 0
+    
+    config EXAMPLE_RLCHN_BTN_DOWN_IO_NUM
+        int "GPIO number for DOWN button"
+        default 1
+    
+    config EXAMPLE_RLCHN_BTN_STOP_IO_NUM
+        int "GPIO number for STOP button"
+        default 2
+    
+    config EXAMPLE_RLCHN_BTN_SELECT_IO_NUM
+        int "GPIO number for STOP button"
+        default 3
+    
+    config EXAMPLE_RLCHN_LED_INDICATOR1_IO_NUM
+        int "GPIO number for LED indicator output for channel 1"
+        default 4
+    
+    config EXAMPLE_RLCHN_LED_INDICATOR2_IO_NUM
+        int "GPIO number for LED indicator output for channel 2"
+        default 10
+    
+    config EXAMPLE_RLCHN_LED_INDICATOR3_IO_NUM
+        int "GPIO number for LED indicator output for channel 3"
+        default 9
+    
+    config EXAMPLE_RLCHN_BTN_LONG_PRESS_TIME_MS
+        int "Long press time in ms to start secondary actions"
+        range 1500 3000
+        default 2000
+        help
+            Long press time in milliseconds is required to start secondary actions 
+            like tilting and flipping.
+
+endmenu