Uses PHP8's constructor property promotion core/Command/App,/Background, and /Broadcast

[fsamapoor]

Following https://github.com/nextcloud/server/pull/38636, https://github.com/nextcloud/server/pull/38637, and https://github.com/nextcloud/server/pull/38638 PRs, I have made the required adjustments to the /core/Command/ namespace as well.

I figured I should split the changes into multiple PRs to make reviewing the changes easier.

This PR refactors /core/Command/App, /core/Command/Background, and /core/Command/Broadcast classes by using PHP8's constructor property promotion to remove redundant lines and make the code cleaner.