apt-key is becoming deprecated

What is/are the relevant URL(s)

https://about.gitlab.com/install/#raspberry-pi-os

Briefly describe the bug

The installation how-to suggests piping a key to apt-key, this is no longer recommended, the key should be saved to /etc/apt/trusted.gpg.d/foo.asc instead. For exmaple see https://www.linuxuprising.com/2021/01/apt-key-is-deprecated-how-to-add.html.

Please provide any relevant screenshots or screencasts

/cc @gl-website