[Feature Request] Add API endpoint to flush the DNS Cache

[skycubeuk]

As a user I would like to be able to flush the dns cache programmatically

When deploying CI/CD pipelines dns records and TTLs can update multiple times in a short period. Being able to clear the DNS cache via an API call would be helpful.

[github-actions[bot]]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[ashmckenzie]

I'm working on a PR for this 🙂