entrypoint plugins fail to load in python 3.9>

**Describe the bug**
entrypoint plugins unable to load in versions older than 3.9

**Environment (please complete the following information):**
- Errbot version: master
- Python version: 3.9 (and earlier)
- Using a virtual environment: yes
- Using Docker: no

**Additional context**

```
ImportError: cannot import name 'SelectableGroups' from 'importlib_metadata'
```
