Adds a config option to specify a maximum message size we'll accept
for an Identify message.
The default is 8KB, the same as go-libp2p - previously we fell back
to the default `maxMessageLength` option of `it-length-prefixed`
which is 4MB.
Also adds a default timeout for reading responses to identify
requests which is used if an AbortSignal is not passed in.
The default timeout also aligns with go-libp2p.