Consider setting allow_device_name_lookup_over_federation to false by default

[anoadragon453]

synapse/docs/sample_config.yaml

Lines 712 to 716 in 7732c49

	# Uncomment to disable device display name lookup over federation. By default, the
	# Federation API allows other homeservers to obtain device display names of any user
	# on this homeserver. Defaults to 'true'.
	#
	#allow_device_name_lookup_over_federation: false

It is undoubtedly a boost to user privacy if device names are not sent over federation to other users. Is there any objection to simply having that by the default (rather than sharing device names)?

Device IDs, which are typically used when debugging encryption-related errors, are still shared out of necessity regardless of this option.

[richvdh]

Agreed, there doesn't seem to be any reason for this to be enabled by default.

Going one step further, why are we only limiting this to federation lookups? Why do we allow any users to see other users' device names in general?

Seems like we should change this; not going to prioritise it for a fix though.