Improve advice for configuring PGP keys for APT

The Debian tool, APT, lets you write GPG keyrings into a file per
trusted source, inside /etc/apt/trusted.gpg.d

Recommend that approach, as it is easier to manage.

Author: Tim Bannister

content/en/docs/setup/production-environment/container-runtimes.md

@@ -81,7 +81,7 @@ sudo apt-get update && sudo apt-get install -y \
 
 ```shell
 # Add Docker's official GPG key:
-curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add --keyring /etc/apt/trusted.gpg.d/docker.gpg -
 ```
 
 ```shell
@@ -244,8 +244,8 @@ cat <<EOF | sudo tee /etc/apt/sources.list.d/devel:kubic:libcontainers:stable:cr
 "deb http://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable:/cri-o:/$VERSION/$OS/ /"
 EOF
 
-curl -L https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/Release.key | sudo apt-key add -
-curl -L https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/Release.key | sudo apt-key add -
+curl -L https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/Release.key | sudo apt-key add --keyring /etc/apt/trusted.gpg.d/libcontainers.gpg -
+curl -L https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/Release.key | sudo apt-key add --keyring /etc/apt/trusted.gpg.d/libcontainers.gpg -
 
 sudo apt-get update
 sudo apt-get install cri-o cri-o-runc
@@ -276,8 +276,8 @@ Then run
 sudo echo "deb https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/ /" > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list
 sudo echo "deb http://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable:/cri-o:/$VERSION/$OS/ /" > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable:cri-o:$VERSION.list
 
-curl -L https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/Release.key | sudo apt-key add -
-curl -L https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/Release.key | sudo apt-key add -
+curl -L https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/Release.key | sudo apt-key add --keyring /etc/apt/trusted.gpg.d/libcontainers.gpg
+curl -L https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/Release.key | sudo apt-key add --keyring /etc/apt/trusted.gpg.d/libcontainers-cri-o.gpg -
 
 sudo apt-get update
 sudo apt-get install cri-o cri-o-runc
@@ -387,7 +387,7 @@ sudo apt-get update && sudo apt-get install -y apt-transport-https ca-certificat
 
 ```shell
 ## Add Docker's official GPG key
-curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add --keyring /etc/apt/trusted.gpg.d/docker.gpg -
 ```
 
 ```shell