TMI2-725 - Remove Contentful slug when unpublishing an advert

[jimpurvisTCO]

Description

https://technologyprogramme.atlassian.net/browse/TMI2-725

Publishing an advert with the same name as a previously published advert causes an error because each advert requires a unique Contentful slug.

Updating the unpublish method so that Contentful slugs are removed and can be used again.

Type of change

Please check the relevant options.

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• This change requires a documentation update.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes:

• Unit Test

• Integration Test (if applicable)

• End-to-End Test (if applicable)

Screenshots (if appropriate):

Please attach screenshots of the change if it is a UI change:

Checklist:

• If I have listed dependencies above, I have ensured that they are present in the target branch.
• I have performed a self-review of my code.
• I have commented my code in hard-to-understand areas.
• I have made corresponding changes to the documentation where applicable.
• I have run cypress tests, and they all pass locally.