Nexus external API: Use stronger types for BgpPeer addresses

[jgallagher]

This is a followup to #10082, and extends the stronger RouterPeerType out from the internal API to the Nexus external API. The primary changes here are:

• Change fields of BgpPeer to give stronger guarantees:
  • BgpPeer::addr is now RouterPeerType instead of Option<IpAddr> (which permitted three distinct representations of "unnumbered": None, Some(0.0.0.0), and Some(::)).
  • BgpPeer::router_lifetime moved from being a top-level field to being nested inside the RouterPeerType::Unnumbered variant, and its type is now RouterLifetimeConfig instead of u16, adding enforcement of bounds.
• Remove BgpPeer::interface_name (closes BgpPeer::interface_name isn't faithfully persisted in the db - we should remove it #10104).
• Define new versions of types that transitively include BgpPeer:
  • BgpPeerConfig
  • SwitchPortSettings
  • SwitchPortSettingsCreate

The bulk of the diff is defining new versions of all these types and unit tests for the conversions they implement. The rest is fallout where these types touch other areas (e.g., datastore methods and bg tasks) and should be relatively straightforward.