Do you know if grafana supports tests that can be run every x minutes, that sends http requests and check response status and body, and then sends status to slack?
I know that datadog offers this.
No Grafana (app) doesn't have that. Grafana is visualization app mainly.
But Grafana ecosystem offers that. For example Grafana Cloud (platform) has Synthetic Monitoring. Or you can use Blackbox exporter and then Grafana can connect to Prometheus, where you will store results from Blackbox exporter.
Generally, you can use any tool which is doing this job and which can store results in Grafana supported time series database.