docs: install: Put APT key into /etc/apt/keyrings

[fumiyas]

Install instruction for Ubuntu/Debian described at https://developer.hashicorp.com/vagrant/install shows:

wget -O - https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
sudo apt update && sudo apt install vagrant

This should be:

wget -O - https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/hashicorp-archive-keyring.gpg
echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
sudo apt update && sudo apt install vagrant

Ubuntu or Debian's sources.list(5) manpage says:

The recommended locations for keyrings are
/usr/share/keyrings for keyrings managed by packages, and
/etc/apt/keyrings for keyrings managed by the system operator.

[Soot3]

Up for this PR, but it looks like this particular page can't be edited from GitHub. Here's a previous issue #13498