apt-key is deprecated and was removed in Debian Trixie

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#### Overview of the Issue

I'm trying to install packer on Debian Trixie, following instructions on https://developer.hashicorp.com/packer/tutorials/docker-get-started/get-started-install-cli selecting "Linux" tab and "Ubuntu/Debian" tab underneath. The first command:
```
curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
```
fails with message:
```
sudo: apt-key: command not found
```
Turns out there is a new way to add gpg keys in Debian. For now, Debian Trixie is still in testing, but this may become a bigger issue upon Debian Trixie release.
This worked for me on Debian Trixie:
```
curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
```
As for deb822 style apt sources, that's another story and would also be nice to have for Debian Trixie and newer.

#### Reproduction Steps

Have a Debian Trixie installation, a VM with minimal install will suffice. Go to https://developer.hashicorp.com/packer/tutorials/docker-get-started/get-started-install-cli select "Linux" tab and "Ubuntu/Debian" tab underneath. Copy the first command from the instructions and run it in Terminal.

### Packer version

N/A

### Simplified Packer Template

N/A

### Operating system and Environment details

Debian Trixie, amd64

### Log Fragments and crash.log files

N/A

Open the Packer installation tutorial linked in the issue and inspect the Linux → Ubuntu/Debian instructions. Reproduce the failure on Debian Trixie, then update the apt-key command to the keyring-based approach shown in the report. Confirm that the documented commands work on Debian Trixie and newer systems.

Written by the indexing model from the issue text.