DER-136 - Restructure and clean up the Credit Default Swaps ontology (WIP)

[ElisaKendall]

Signed-off-by: Elisa Kendall [email protected]

Description

1. Created the concept of a credit derivative in derivatives basics, added a subclass relation between credit derivative and total return swap, and made some preliminary changes to credit default swaps per FCT discussion on 10/11/2022

Fixes: #1843 / DER-136

Checklist:

• [x] I'm familiar with the FIBO developer quide. My contribution meets all the requirements described there.
• [x] My contribution follows the principles of best practices for FIBO.
• [x] My changes have been reconciled with latest master and no merge conflicts remain.
• [x] This PR is related to exactly one issue. The issue is referenced by using a GitHub keyword such as "fixes", "closes", or "resolves".
• [x] Hygiene tests have been applied by a PR with "(WIP)" in title.
• [x] The issue has been tested locally using a reasoner (for ontology changes).