Allow specifying allowed source address(es)

Nobody has claimed this yet.

Currently, it's possible to specify _listen_ addresses, but not source addresses for dials. It would be nice to be able to actually specify _source_ addresses.

Specifically:

1. An initial implementation would allow specifying a _single_ allowed source address. This option would need to be piped through to all transports and transports would need to be updated to obey it. Unfortunately, this would likely prevent, e.g., loopback dials. This trivial from a purely technical perspective, but we don't currently have a nice way to _reliably_ pipe this information through from go-libp2p to the individual transports.
2. After the initial implementation, support for _multiple_ allowed source addresses. Unfortunately, this is significantly more complicated to implement.

At the moment, the best solution here is to sandbox your application (i.e., use a network namespace) so libp2p simply doesn't have access to interfaces it's not allowed to use. Furthermore, restricting the application to a single interface/source address isn't something go-libp2p can actually _enforce_ (i.e., some transports may ignore the setting and/or have bugs). Even if/when this feature is implemented, users should continue to sandbox libp2p if they don't want it to use/see some set of interfaces.

See https://github.com/libp2p/go-libp2p/issues/1063 for motivation.

Start by reading the motivation in issue #1063 and tracing how listen-address configuration reaches each transport in go-libp2p. Define how a single allowed source address would be propagated and enforced across transports before considering multiple addresses; done requires transport-wide support with documented limitations.

Written by the indexing model from the issue text.