feat: attach vector container to additional docker networks

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`.

plugins/logs/set.go

@@ -4,6 +4,9 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
+	"strings"
+
+	"github.com/dokku/dokku/plugins/common"
 )
 
 func validateSetValue(appName string, key string, value string) error {
@@ -11,6 +14,10 @@ func validateSetValue(appName string, key string, value string) error {
 		return validateMaxSize(appName, value)
 	}
 
+	if key == "vector-networks" {
+		return validateVectorNetworks(appName, value)
+	}
+
 	if key == "vector-sink" {
 		return validateVectorSink(appName, value)
 	}
@@ -56,3 +63,30 @@ func validateVectorSink(appName string, value string) error {
 
 	return nil
 }
+
+func validateVectorNetworks(appName string, value string) error {
+	if value == "" {
+		return nil
+	}
+
+	for _, name := range strings.Split(value, ",") {
+		name = strings.TrimSpace(name)
+		if name == "" {
+			return errors.New("Invalid vector-networks value, empty entry in comma-separated list")
+		}
+
+		if name == "bridge" {
+			return errors.New("Invalid vector-networks value, \"bridge\" is attached by default and must not be listed")
+		}
+
+		result, err := common.CallExecCommand(common.ExecCommandInput{
+			Command: common.DockerBin(),
+			Args:    []string{"network", "inspect", name},
+		})
+		if err != nil || result.ExitCode != 0 {
+			return fmt.Errorf("Network %q does not exist", name)
+		}
+	}
+
+	return nil
+}