During a refresh of the supported features via the DNS TXT record,
cloudflared would update the internal feature list, but would not
propagate this information to the edge during a new connection.
This meant that a situation could occur in which cloudflared would
think that the client's connection could support datagram V3, and
would setup that muxer locally, but would not propagate that information
to the edge during a register connection in the `ClientInfo` of the
`ConnectionOptions`. This meant that the edge still thought that the
client was setup to support datagram V2 and since the protocols are
not backwards compatible, the local muxer for datagram V3 would reject
the incoming RPC calls.
To address this, the feature list will be fetched only once during
client bootstrapping and will persist as-is until the client is restarted.
This helps reduce the complexity involved with different connections
having possibly different sets of features when connecting to the edge.
The features will now be tied to the client and never diverge across
connections.
Also, retires the use of `support_datagram_v3` in-favor of
`support_datagram_v3_1` to reduce the risk of reusing the feature key.
The `dv3` TXT feature key is also deprecated.
Closes TUN-9291
ce27840573