Load completions from the host

[josecastillolema]

Is your feature request related to a problem? Please describe.
Today it is not possible to load (ba)sh completions from the host, looks like /usr/share/bash-completion is banned.

⬢ [fedora-toolbox:39] > flatpak-spawn --host /usr/share/bash-completion/completions/podman
Portal call failed: Failed to start command: Failed to execute child process “/usr/share/bash-completion/completions/podman” (Permission denied)

Describe the solution you'd like
I would like to be able to import those completions without the need of installing the corresponding packets on each toolbox container.