fix: CHANGELOG.MD uses the deprecated editor.swagger.io

[Kevsy]

Problem description

CHANGELOG.MD uses the deprecated editor.swagger.io to render the OAS YAML, which will not work:

https://editor.swagger.io/?url=https://raw.githubusercontent.com/camaraproject/QoSBooking/r1.2/code/API_definitions/qos-booking.yaml

Expected behavior

Change the URL to use the official CAMARA Swagger UI:
https://camaraproject.github.io/swagger-ui/?url=https://raw.githubusercontent.com/camaraproject/QoSBooking/r1.2/code/API_definitions/qos-booking.yaml

(this applies to both API links)

Alternative solution

Additional context

[hdamker]

After fix, update the release description r1.2 in GitHub with the same change.

[Kevsy]

After fix

PR #60 is made, once merged by a release-management-reviewer I will update the r1.2 release description