Allow sprintf field reference for port property

[bczifra]

The code expects the port property to be specified as a number. If you specify port => "%{[port]}" then it will throw the following error:

Here is the error message in the log:
[2021-11-11T16:08:05,089][ERROR][logstash.outputs.tcp ] Invalid setting for tcp output plugin:

output {
tcp {
# This setting must be a number
# Expected number, got "%{[port]}" (type %{[port]})
port => "%{[port]}"
...
}
}
[2021-11-11T16:08:05,094][ERROR][logstash.agent ] Failed to execute action

It would be useful to be able to specify this value based on the event properties in the manner shown above.