Minimal devcontainer definitions aimed at working with vscode flatpak and podman-remote

Prerequisites

Visual Studio Code flatpak needs the com.visualstudio.code.tool.podman extension.
Set podman-remote as the Docker executable in Visual Studio Code. In the settings.json add:
```
"dev.containers.dockerPath": "/app/tools/podman/bin/podman-remote"
```
Allow vscode to access xdg-run/podman in filesystem permissions.
The podman.socket service needs to be running at the user level.
- Start it with:
```
systemctl --user start podman.socket
```
- Or make it persisten between reboots:
```
systemctl --user enable --now podman.socket
```
SELinux's enforcing policy may lead to errors accessing files in the container.