Add gpg-agent package, required by coverage job

Author: Bronek

docker/debian/Dockerfile

@@ -43,6 +43,7 @@ pkgs+=(dpkg-dev)        # Required packaging tool.
 pkgs+=(file)            # Required packaging tool.
 pkgs+=(git)             # Required build tool.
 pkgs+=(gpg)             # Dependency for tools requiring signing or encrypting/decrypting.
+pkgs+=(gpg-agent)       # Dependency for tools requiring signing or encrypting/decrypting.
 pkgs+=(jq)              # Pretty printing.
 pkgs+=(libc6-dev)       # Required build tool.
 pkgs+=(ninja-build)     # Required build tool.

docker/rhel/Dockerfile

@@ -18,6 +18,7 @@ pkgs+=(cmake)            # Required build tool.
 pkgs+=(file)             # Required packaging tool.
 pkgs+=(git)              # Required build tool.
 pkgs+=(gpg)              # Dependency for tools requiring signing or encrypting/decrypting.
+pkgs+=(gpg-agent)        # Dependency for tools requiring signing or encrypting/decrypting.
 pkgs+=(jq)               # Pretty printing.
 pkgs+=(libstdc++-static) # Required to statically link libraries into rippled.
 pkgs+=(ninja-build)      # Required build tool.

docker/tools-rippled/Dockerfile

@@ -28,6 +28,7 @@ pkgs+=(ca-certificates) # Enable TLS verification for HTTPS connections by provi
 pkgs+=(curl)            # Dependency for tools requiring downloading data.
 pkgs+=(git)             # Required build tool.
 pkgs+=(gpg)             # Dependency for tools requiring signing or encrypting/decrypting.
+pkgs+=(gpg-agent)       # Dependency for tools requiring signing or encrypting/decrypting.
 pkgs+=(jq)              # Pretty printing.
 pkgs+=(pipx)            # Package manager for Python applications.
 pkgs+=(wget)            # Required build tool.

docker/ubuntu/Dockerfile

@@ -32,6 +32,7 @@ pkgs+=(dpkg-dev)        # Required packaging tool.
 pkgs+=(file)            # Required packaging tool.
 pkgs+=(git)             # Required build tool.
 pkgs+=(gpg)             # Dependency for tools requiring signing or encrypting/decrypting.
+pkgs+=(gpg-agent)       # Dependency for tools requiring signing or encrypting/decrypting.
 pkgs+=(jq)              # Pretty printing.
 pkgs+=(libc6-dev)       # Required build tool.
 pkgs+=(ninja-build)     # Required build tool.