Provide a plug-in for serial port data.

## Feature Request
I wasn't able to find in input plug-in for data coming from a serial port
### Proposal:
Could it be possible to provide such a plug-in that reads data from the serial port according to a given pattern?
### Current behavior:
Currently no plug-in available, at least not under the keyword serial.
### Desired behavior:
Provide a new plug in or add the keyword "serial" to and eventually existing plug-in that could do the job.
### Use case:
Many measuring instruments are providing data over a serial port.
The serial port is also the primary, communication wait for microcontrollers like the Arduino.
That way of receiving data should not be missing in Telegraf.

Start by reviewing Telegraf's existing input plug-ins and how they handle external data sources. Clarify the serial-port protocol, platform support, configuration format, and pattern-matching behavior before implementation; done means a documented serial input plug-in or an explicitly suitable existing plug-in with tests for representative instrument data.

Written by the indexing model from the issue text.