Update deprecated arduino-language-server docs

[Arian8j2]

arduino-language-server dropped supporting sketch.json so the example in docs doesn't work, instead you have to create sketch.yaml that also has different configuration keywords, for example this was old sketch.json format:

{
  "cpu": {
    "fqbn": "arduino:avr:uno",
    "port": "serial:///dev/ttyACM0"
  }
}

now in sketch.yaml format it's like this:

default_fqbn: arduino:avr:uno
default_port: /dev/ttyACM0

also arduino-cli board attach -p /dev/ttyACM0 test.ino command does not generate the default_fqbn: arduino:avr:uno part, it just generates default_port: /dev/ttyACM0, you need to explicitly specify board in attach command, example: arduino-cli board attach -p /dev/ttyACM0 -b arduino:avr:uno test.ino to generate ready to use sketch.yaml for lsp to work.

i couldn't find the exact commit that they dropped supporting sketch.json, but found a comment on one of issues from official arduino dev arduino/arduino-language-server#80 (comment)

[github-actions]

Do not change server_configurations.md directly. Edit the lua source file instead. See https://github.com/neovim/nvim-lspconfig/blob/master/CONTRIBUTING.md#generating-docs