Add support for custom MAVLink dialects at runtime

[roby2014]

At the moment, mavlink::common::MavMessage is used to de/serialize MavLink messages.
The rust-mavlink crate depends on a trait implementation of Message in order to calculate crc's, depending on the message fields, etc.

The goal here is to provide somehow an option for custom MAVLink dialects.

1. A possible solution would be to provide the .xml schema as configuration, but that would require an additional compilation of the plugin to generate Rust structures.
2. A good suggestion (by @tjrmarques) was to load the trait implementation via a provided shared library, e.g:

[
        {
          endpoint: "udpout:0.0.0.0:1337",
          mavlink_dialect: "/home/roby/custom_mav_dialect.so",
          mavlink_version: 2,
        },
        {
          endpoint: "udpout:0.0.0.0:1337",
          mavlink_version: 2,
          /// mavlink::common::MavMessage will be used as default when not provided
        },
]

3. Use something like this: https://docs.rs/mavinspect/latest/mavinspect/index.html