Add support for dual-stack networking (ipv4 + ipv6)

**Is your feature request related to a problem? Please describe.**
`matrix-content-scanner-python` only connects [to 1 listener](https://github.com/element-hq/matrix-content-scanner-python/blob/main/src/matrix_content_scanner/httpserver.py#L145-L151). This prevents it from running on both ipv4 and ipv6.

**Describe the solution you'd like**
Add a list of listeners instead of a single one in https://github.com/element-hq/matrix-content-scanner-python/blob/367a8c56ed6f95c5f36aa8ac035725af2972e6c5/config.sample.yaml#L16-L19

**Describe alternatives you've considered**
Run 2 matrix-content-scanner processes in parallel.