Add simple Ruby server example

[kou]

fix apache/arrow#40479

[ianmcook]

Thanks @kou!

I tested this with all the client examples. The only problem I found was with the C GLib client:

When I run the C GLib client with this this Ruby server, the server prints this message:

::1 - - [12/Mar/2024:09:14:43 -0400] "GET / HTTP/1.1" 200 - 0.8649
[2024-03-12 09:14:44] ERROR Errno::ECONNRESET: Connection reset by peer @ io_fillbuf - fd:18 
	/opt/homebrew/lib/ruby/gems/3.3.0/gems/webrick-1.8.1/lib/webrick/httpserver.rb:82:in `eof?'
	/opt/homebrew/lib/ruby/gems/3.3.0/gems/webrick-1.8.1/lib/webrick/httpserver.rb:82:in `run'
	/opt/homebrew/lib/ruby/gems/3.3.0/gems/webrick-1.8.1/lib/webrick/server.rb:310:in `block in start_thread'

[ianmcook]

Can you add a .gitignore with Gemfile.lock please?

[kou]

Ah, it's happen because GLib client uses keep-alive and Ruby's HTTP server is sensitive for disconnection check of keep-alive connection.

I'll disable keep-alive of GLib client.

[kou]

I've add missing .gitignore. Good catch!

[kou]

GLib client: #20

[ianmcook]

Thanks!