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

[gaelgatelement]

Is your feature request related to a problem? Please describe.
matrix-content-scanner-python only connects to 1 listener. 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

matrix-content-scanner-python/config.sample.yaml

Lines 16 to 19 in 367a8c5

	# Configuration for hosting the HTTP(S) API.
	web:
	host: 127.0.0.1
	port: 8080

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

[anoadragon453]

No customer commitment behind this, but it's something that SPT want by the end of Q3 (so end of October). They have a plan to support ipv4+ipv6 for all components by end-of-Q3.