refactor: Use sdkconfig.defaults for ESP-IDF example

ESP-IDF allows projects to specify a sdkconfig.defaults values which contain
preset values for configuration options of relevance to the project. This
allows ESP-IDF to use those presets while supplying default values for all
other configuration options, when generting the final sdkconfig file.

Changes:

- Ran `idf.py save-defconfig` to find non-default value configs. Saved
relevant ones to `sdkconfig.defaults`
- Removed `sdkconfig` file
- Added `sdkconfig` to `.gitignore` as ESP-IDF will generate a `sdkconfig`
based on `sdkconfig.defaults` when building.

examples/NonArduino/ESP-IDF/.gitignore

@@ -1,3 +1,4 @@
 # generated by ESP-IDF
 managed_components/
 dependencies.lock
+sdkconfig

examples/NonArduino/ESP-IDF/README.md

@@ -8,3 +8,4 @@ This example shows how to use RadioLib as ESP-IDF component, without the Arduino
 * `main/EspHal.h` - RadioLib HAL example implementation
 * `main/idf_component.yml` - declaration of the RadioLib dependency for this example
 * `main/main.cpp` - the example source code
+* `sdkconfig.defaults` - List of preset configuration option values for ESP-IDF. All other options use default values provided by ESP-IDF.

examples/NonArduino/ESP-IDF/sdkconfig.defaults

@@ -0,0 +1,2 @@
+# Increase FreeRTOS tick rate to 1000 Hz
+CONFIG_FREERTOS_HZ=1000