Adds a new global `vector-networks` property on the logs plugin that takes a comma-separated list of Docker networks. When set, the rendered compose file declares each network plus `bridge` as external and joins them on the vector service, so `docker compose up` reconciles attachments on every `logs:vector-start`. When unset, the existing `network_mode: bridge` template is preserved unchanged. The value is validated against `docker network inspect` at set time, rejects the reserved `bridge` entry, and is surfaced in `dokku logs:report` via `--logs-vector-global-networks`.
Using compose instead of manual docker calls allows folks to customize the vector container by using a custom compose.yml template file. This opens us up to more customizations while aligning container management with how we do other external containers (such as for the proxy plugins).
Refs #5784
