What is this feature?
Allows the creation of alert rules with mimirtool in a specified folder.
Why do we need this feature?
Currently, the APIs for mimirtool create namespaces and rule groups in the root folder without the ability to set a custom folder. For example, it could be a special "Imported" folder, etc.
This PR makes it possible with a special header: mimirtool ... --extra-headers="X-Grafana-Alerting-Folder-UID=123". If it's not present, the root folder is used, otherwise, the specified one is used.
mimirtool does not support nested folder structures, while Grafana allows folder nesting. To keep compatibility, we return only direct child folders of the working folder (as namespaces) with rule groups and rules that are directly in these child folders as if there are no nested folders.
For example, given this folder structure in Grafana:
```
grafana/
├── production/
│ ├── service1/
│ │ └── alerts/
│ └── service2/
└── testing/
└── service3/
```
If the working folder is "grafana":
Only namespaces "production" and "testing" are returned
Only rule groups directly within these folders are included
If the working folder is "production":
- Only namespaces "service1" and "service2" are returned
Only rule groups directly within these folders are included
Integration tests
This directory contains Grafana server integration tests.