docs: Rename ap-port option as ap_port

[Jiogo18]

#1420 introduced the option ac_port to specify the port used by librespot.
This option works great, except when following the documentation and example only.

• The option is named ap-port in librespot.
• The option is named ap_port in ConfigValues.
• However, the option is named ac-port in the documentation and in feat(config): Allow users to set AP port #1420, which doesn't work, as described below.

In ncspot/config.toml:

• ❌ ap-port = 443 does nothing, librespot uses port 4070
• ✅ ap_port = 443 librespot uses HTTPS

Describe your changes

Rename ap-port option by ap_port in the documentation.

Issue ticket number and link

Checklist before requesting a review

• Documentation was updated (i.e. due to changes in keybindings, commands, etc.)
• Changelog was updated with relevant user-facing changes (eg. not dependency updates,
  not performance improvements, etc.)

Before merge

Should the changelog be updated too?
Changelog of 1.1.1 contains ap-port, which is misleading.

[ThomasFrans]

I'd update the changelog as well. When I added it, I based it on the keepachangelog format which states that changes to earlier parts are encouraged if they improve the changelog. It's nice if users read the changelog that it kind of serves as "brief documentation" for new features 🙂

[hrkfdn]

Thank you, merged :)