Update Schema to have cascading deletion of Posts and Comments

User Story

User should be able to delete posts and all comments

[Add your technical tasks here]

Before PR

[ ] Have tested locally using ThunderClient/Postman/etc.
[ ] For any new APIs, have documented in the README.md
[ ] Have included and tested any required schema changes
[ ] Have handled all error cases (try/catch, checked user input, etc.)
[ ] Error messages are consistent with the rest of the code
[ ] Correct HTTP Response codes and verbs are used
[ ] Code confirms to the existing style and structure
[ ] No warnings or errors are reported when using the API
[ ] If modifying an existing API the client app already uses, have verified locally the client app still works as expected with changes
[ ] If adding a new API, any developers working on the client have reviewed the request params and expected responses

After PR Merge

[ ] Have verified the API works on the deployed build using ThunderClient/Postman/etc.
[ ] Have verified any required schema updates have been applied cleanly
[ ] If modifying an existing API the client app already uses, have verified the deployed client app still works as expected