Update react-table to v8 (#2131)

Updating react-table to v8. 
- Migrating the existing table to v8
- Preserving the visuals and logic

What's done?
- Cell components are moved under `Cells` folder
- Old styles for react-table-6 is removed.
- Old types are removed
- All logic was preserved
- Some cell components are removed for simplicity


Fixes: https://github.com/grafana/oss-big-tent-squad/issues/125

src/datasource/types.ts

@@ -108,6 +108,7 @@ export interface ProblemDTO {
   datasource?: DataSourceRef | string;
   comments?: string;
   host?: string;
+  hostInMaintenance?: boolean;
   hostTechName?: string;
   proxy?: string;
   severity?: string;