Make bootcfg sense optional (#1051)

* Make bootcfg sense optional

In case we're only interested in non-lockout-prone options, like NKRO

docs/en/boot.md

@@ -19,9 +19,8 @@ configuration.
 from kmk.bootcfg import bootcfg
 
 bootcfg(
-    # required:
-    sense: [microcontroller.Pin, digitalio.DigitalInOut],
     # optional:
+    sense: Optional[microcontroller.Pin, digitalio.DigitalInOut] = None,
     source: Optional[microcontroller.Pin, digitalio.DigitalInOut] = None,
     autoreload: bool = True,
     boot_device: int = 0,
@@ -45,8 +44,8 @@ they may differ from board specific defaults.
 #### `sense`
 `sense` accepts either uninitialized `Pin`s or `DigitalInOut` instances for
 maximum flexibility.
-The boot configuration is only applied if `sense` reads `True` or "high", and
-skipped if it reads `False` or "low".
+The lockout-prone subset of boot configuration is only applied if `sense` reads `True` or "high", and
+skipped if it reads `False` or "low". The latter is also true if `sense` is not provided.
 If `sense` is an uninitialized `Pin`, it'll be configured as pulled-up input; it
 wont be further configured if it is a `DigitalInOut`.
 
@@ -81,6 +80,7 @@ for details.
 
 #### `cdc_console`
 This will enable or disable the USB endpoint for the serial console with REPL.
+**Caution**: If erroneous `sense` parameter is provided, changing this might make recovery problematic.
 
 
 #### `cdc_data`
@@ -122,6 +122,7 @@ hid endpoint.
 #### `storage`
 Disable storage if you don't want your computer to go "there's a new thumb drive
 I have to mount!" every time you plug in your keyboard.
+**Caution**: If erroneous `sense` parameter is provided, changing this might make recovery problematic.
 
 
 #### `usb_id`

kmk/bootcfg.py

@@ -9,7 +9,7 @@
 
 
 def bootcfg(
-    sense: [microcontroller.Pin, digitalio.DigitalInOut],
+    sense: Optional[microcontroller.Pin, digitalio.DigitalInOut] = None,
     source: Optional[microcontroller.Pin, digitalio.DigitalInOut] = None,
     autoreload: bool = True,
     boot_device: int = 0,
@@ -86,9 +86,9 @@ def bootcfg(
 
         usb_cdc.enable(data=True)
 
-    # sense pulled low -> Skip boot configuration that may disable debug or
-    # rescue facilities.
-    if not sense.value:
+    # sense not provided or pulled low -> Skip boot configuration that may
+    # disable debug or rescue facilities.
+    if sense is None or not sense.value:
         return False
 
     # Entries for serial console (REPL) and storage are intentionally evaluated