implement cogs feature

[masteradhoc]

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Changes proposed in this Pull Request:

WooCommerce Core is getting the Cost of Goods Sold (COGS) feature soon. (currently behind a feature flag)
We should allow to also auto generate COGS Values inside Smooth Generator.
Approach automatically generates it for simple and variable products while deducting a random 15-60% from the regular price

Closes #175 .

How to test the changes in this Pull Request:

0. activate the COGS feature at /wp-admin/admin.php?page=wc-settings&tab=advanced&section=features if not yet done
1. apply this PR
2. generate 25 random products
3. check for simple and variable products if the COGS number was generated correctly

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

Changelog entry

implement cost of good sold (cogs) generation

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

FOR PR REVIEWER ONLY:

• I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.