Create custom field for shipping method in Drupal Commerce 2

I'm trying to add a new field called Opening Hours for commerce_shipping_method bundle. I'm having hard time finding examples how to do this and those I tried didn't really work for me. In fact, not even adding a simple numeric field worked for me.

I have 2 YML files in a custom module where I define the testing numeric field.

custom_module.field_instance.yml

langcode: en
status: true
dependencies:
  config:
    - field.storage.commerce_shipping_method.field_opening_hours_x
id: commerce_shipping_method.commerce_shipping_method.field_opening_hours_x
field_name: field_opening_hours_x
entity_type: commerce_shipping_method
bundle: commerce_shipping_method
label: 'Test Numeric Field'
description: 'A test field'
required: false
default_value: {  }
default_value_callback: ''
settings: {  }
third_party_settings: {  }
deleted: false

custom_module.field_storage.yml

langcode: en
status: true
dependencies:
  module:
    - commerce_shipping
id: commerce_shipping_method.field_opening_hours_x
field_name: field_opening_hours_x
entity_type: commerce_shipping_method
type: decimal
module: number
settings:
  precision: 2
locked: false
cardinality: 1
translatable: true
indexes: {  }
persist_with_no_fields: true
custom_storage: false

When I install this module and go to edit my shipping method ( /admin/commerce/shipping-methods/manage/2?destination=/admin/commerce/shipping-methods ), the extra field is not present.

Any help or pointers to the right docs on how to do this would be appreciated.

After some help from the slack commerce community and reviewing a Drupal article on field definitions, I came up with the following resolution:

my_commerce.module

Here is where the definition that's shown on form page goes. It didn't work if I simply used it in the update hook (second file below), so I had to duplicate the definition in my .module file as well.

/**
 * Implements hook_entity_base_field_info().
 */
function my_commerce_entity_base_field_info( EntityTypeInterface $entity_type ) {
  $fields = array();

  // add opening hours text area field to commerce shipping methods
  if ($entity_type->id() === 'commerce_shipping_method') {
    $fields['opening_hours'] = BaseFieldDefinition::create( 'text_long' )
      ->setLabel( t( 'Opening Hours' ) )
      ->setDescription( t( 'You can provide opening hours to physical pickup/payments points.' ) )
      ->setRevisionable(true )
      ->setTranslatable( true )
      ->setSetting( 'target_type', 'commerce_shipping_method' )
      ->setSetting( 'handler', 'default' )
      ->setSetting( 'handler', 'default' )
      ->setDisplayOptions('form', array(
        'type' => 'text_textarea',
        'settings' => array(
          'display_label' => true,
        ),
      ))
      ->setDisplayOptions('view', [
        'label' => 'hidden',
        'type' => 'text_long',
        'weight' => 0,
      ])
      ->setCardinality( 1 )
      ->setDisplayConfigurable( 'form', true );
  }

  return $fields;
}

my_commerce.install

While the .module file will show the Opening Hours textarea on the opening hours form, this part handles saving the value for that field into the database.

/**
 * Add opening hours field to all shipping methods.
 */
function my_commerce_update_9006() {
  $field_storage_definition = BaseFieldDefinition::create( 'text_long' )
    ->setLabel( t( 'Opening Hours' ) )
    ->setDescription( t( 'You can provide opening hours to physical pickup/payments points.' ) )
    ->setRevisionable(true )
    ->setTranslatable( true )
    ->setSetting( 'target_type', 'commerce_shipping_method' )
    ->setSetting( 'handler', 'default' )
    ->setDisplayOptions('form', array(
      'type' => 'text_textarea',
      'settings' => array(
        'display_label' => true,
      ),
    ))
      ->setDisplayOptions('view', [
        'label' => 'hidden',
        'type' => 'text_long',
        'weight' => 0,
      ])
    ->setCardinality( 1 )
    ->setDisplayConfigurable( 'form', true );

  \Drupal::entityDefinitionUpdateManager()
    ->installFieldStorageDefinition('opening_hours', 'commerce_shipping_method', 'commerce_shipping_method', $field_storage_definition);
}