portablectl: add page (#11212)

pages/linux/portablectl.md

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+# portablectl
+
+> A systemd utility for managing and deploying portable service images on Linux systems.
+> More information: <https://www.freedesktop.org/software/systemd/man/portablectl.html>.
+
+- List available portable service images discovered in the portable image search paths:
+
+`portablectl list`
+
+- Attach a portable service image to the host system:
+
+`portablectl attach {{path/to/image}}`
+
+- Detach a portable service image from the host system:
+
+`portablectl detach {{path/to/image|image_name}}`
+
+- Display details and metadata about a specified portable service image:
+
+`portablectl inspect {{path/to/image}}`
+
+- Check if a portable service image is attached to the host system:
+
+`portablectl is-attached {{path/to/image|image_name}}`