changelog: Add section for Customer Group Pricing
changelog: Add section for Customer Group Pricing

Should be its own section, since Customer Group Pricing is not part of
core, but its own app.

Refs SHOOP-2101

hrayr-artunyan/shuup,suutari/shoop,shawnadelic/shuup,hrayr-artunyan/shuup,shoopio/shoop,shawnadelic/shuup,shoopio/shoop,suutari-ai/shoop,shawnadelic/shuup,hrayr-artunyan/shuup,suutari-ai/shoop,shoopio/shoop,suutari/shoop,suutari/shoop,suutari-ai/shoop