meta-digi-containers: add explicit runtime dependencies for the manager

Our container managers depends on podman and LXC runtime tools, so add
that dependency.
As we provide a trimmed version of both tools (to keep the rootfs minimal),
add a variable so it is easily configurable by customers.

Signed-off-by: Isaac Hermida <isaac.hermida@digi.com>

meta-digi-containers/README.md

@@ -7,9 +7,18 @@ This layer provides:
 - `dey-image-container` to generate container artifacts
 - `dey-image-container-manager` to run and manage Podman/LXC containers on target
 
-`dey-image-container-manager` installs dedicated `lxc-trimmed` and `podman-trimmed`
+`cc-container-mng` depends on the container runtime packages listed in
-recipes, so it does not require `DISTROOVERRIDES` changes in `local.conf`
+`CONTAINERS_BACKEND_TOOLS`, which defaults to `podman lxc`. Override it to select
-and does not affect other DEY images built in the same environment.
+different runtimes or a single engine, for example:
+
+```bitbake
+CONTAINERS_BACKEND_TOOLS = "podman-trimmed lxc-trimmed"
+CONTAINERS_BACKEND_TOOLS = "podman-trimmed"
+CONTAINERS_BACKEND_TOOLS = "lxc"
+```
+
+`dey-image-container-manager` overrides `CONTAINERS_BACKEND_TOOLS` to install
+the trimmed runtime packages to keep the image smaller.
 
 The layer explicitly depends on `meta-virtualization`, and
 `dey-image-container-manager`

meta-digi-containers/recipes-containers/cc-container-mng/cc-container-mng_1.0.0.bb

@@ -27,7 +27,10 @@ SYSTEMD_AUTO_ENABLE ?= "enable"
 
 DEPENDS += "python3-pip-native"
 
+CONTAINERS_BACKEND_TOOLS ?= "podman lxc"
+
 RDEPENDS:${PN} += " \
+    ${CONTAINERS_BACKEND_TOOLS} \
     python3-core \
     python3-asyncio \
     python3-json \

meta-digi-containers/recipes-core/images/dey-image-container-manager.bb

@@ -77,10 +77,9 @@ CORE_TOOLS = " \
 "
 
 # Tools to manage containers
+CONTAINERS_BACKEND_TOOLS:pn-cc-container-mng = "lxc-trimmed podman-trimmed"
 CONTAINER_MANAGEMENT = " \
 	cc-container-mng \
-	lxc-trimmed \
-	podman-trimmed \
 "
 
 # Keep the systemd/udev hotplug support packages that are otherwise