Feat: adjust fields for ECS compatibility

[kares]

Since the plugin was setting fields that conflict with ECS schema, we're introducing an ecs_compatibility mode.

• legacy host becomes [host][name] in ECS mode
• the socket file path is now [file][path] in ECS mode

Also, fixed i-var name and logged message as reported in #25

NOTE: CI failures are not new - 6.x has been broken for a long time.
The problematic spec assumes a client socket blocking from readpartial (while the server keep the socket open wout writing anything) to be interruptible on client_socket.close - this is not the case and the only reason the spec does not hang CI is due the teardown closing the server socket -> leads to a EOF from the readpartial.
Also the potential use of timeout is problematic - a proper implementation would be to use select with a timeout and check for stopping periodically.

[karenzone]

Left some suggestion inline for your consideration. Version bump will be required to get these changes picked up and added to the documentation. Thanks!

[yaauie]

The ECS-related changes LGTM, so in that since I'm approving this PR.

I also appreciated your analysis on why this has been failing CI in 6.x for a long time. I agree that using IO::select with a timeout is a less-troublesome approach than Timeout::timeout, and it would be nice to fix the specs for 6.x before 6.x is EOL'd. Can this be done in a follow-up effort?