Add graphql mutations to delete builds and invocations

[trey-ivy]

When running in a production environment with lots of invocations, builds and targets, the database can bloat up pretty big pretty quickly, which has storage cost and performance implications. A mechanism is needed to manage the size of the database.

This PR adds a few graphql API endpoints to manage invocations and builds. It also updates the backend schema to include cascading delete relationships as appropriate.

New Methods:

• deleteInvocation (By Id)
• deleteBuild (By Id)
• deleteInvocationsBefore(takes a time, deletes all invocations that finished before that time)
• deleteBuildsBefore(takes a time, deletes all builds that started before that time)

This process does not currently support blob cleanup. I plan to add that in a future PR. Also in a future PR I plan to add an option to configure and run a process on a schedule to automate this task

Also updates golden files as appropriate