Make card_number more central for CORE API -> Rattail importers

let's track that as (effectively) `Customer.corepos_card_number` and
use that when possible for importer key

rattail_corepos/db/alembic/versions/ae74c537ea51_add_customer_card_number.py

@@ -0,0 +1,39 @@
+# -*- coding: utf-8; -*-
+"""add customer.card_number
+
+Revision ID: ae74c537ea51
+Revises: d6a0f21a6a94
+Create Date: 2023-06-05 19:04:25.574077
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'ae74c537ea51'
+down_revision = 'd6a0f21a6a94'
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+import rattail.db.types
+
+
+
+def upgrade():
+
+    # corepos_customer
+    op.alter_column('corepos_customer', 'corepos_account_id',
+               existing_type=sa.INTEGER(),
+               nullable=True)
+    op.add_column('corepos_customer', sa.Column('corepos_card_number', sa.Integer(), nullable=True))
+    op.add_column('corepos_customer_version', sa.Column('corepos_card_number', sa.Integer(), autoincrement=False, nullable=True))
+
+
+def downgrade():
+
+    # corepos_customer
+    op.drop_column('corepos_customer_version', 'corepos_card_number')
+    op.drop_column('corepos_customer', 'corepos_card_number')
+    op.alter_column('corepos_customer', 'corepos_account_id',
+               existing_type=sa.INTEGER(),
+               nullable=False)