Raise genesis's bus where the nats module keeps it, so adopting it keeps it (hq issue 590, ADR 0333)

The bundle raised the bus as mesh-broker on docker volumes; the catalogue's nats module keeps it as
mesh-broker-nats on directories of the machine, so the broker step refused rather than raise a second
bus, and genesis stopped at step 18 of 24.

The bundle now raises mesh-broker-nats with its configuration and user list in /var/lib/nats-module/conf,
its streams in /var/lib/mesh-broker-nats and its certificate in /var/lib/mesh-broker-tls, published on the
node's bus port. The broker step holds that layout to the module's manifest field by field before
registering anything, says the one restart onto the module's image, and waits until the bus runs that image
and its monitor answers. The installer's bridge writes the composed users at the module's bus-users path and
signals mesh-broker-nats. The bundle's bus configuration and user list are seeds, so a re-run after the
adoption does not put the bundle's one user back over the module's.

internal/bootstrap/bootstrap.go

@@ -734,7 +734,7 @@ func Run(ctx context.Context, o Options, d Deps, say func(string)) (Result, erro
 
 	// ---- broker ---------------------------------------------------------------------------
 	say("broker — the foundation's bus, adopted as the nats module: one bus, not two")
-	if err := InstallBroker(ctx, o, permanentControl, rewritten.Declaration, say); err != nil {
+	if err := InstallBroker(ctx, o, permanentControl, rewritten.Declaration, d.Fetch, say); err != nil {
 		return result, failed(StepBroker, err)
 	}