treewide: switch to gomod and bump everything

This switches version resolution from fietsje to gomod and updates
all Go dependencies. It also bumps rules_go (required by gVisor) and
switches the Gazelle naming convention from go_default_xxx to the
standard Bazel convention of the default target having the package
name.

Since Kubernetes dropped upstream Bazel support and doesn't check in
all generated files I manually pregenerated the OpenAPI spec. This
should be fixed, but because of the already-huge scope of this CL
and the rebase complexity this is not in here.

Change-Id: Iec8ea613d06946882426c2f9fad5bda7e8aaf833
Reviewed-on: https://review.monogon.dev/c/monogon/+/639
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
Reviewed-by: Leopold Schabel <leo@nexantic.com>
diff --git a/metropolis/node/core/consensus/testhelpers.go b/metropolis/node/core/consensus/testhelpers.go
index 627a278..32bbc46 100644
--- a/metropolis/node/core/consensus/testhelpers.go
+++ b/metropolis/node/core/consensus/testhelpers.go
@@ -4,7 +4,7 @@
 	"context"
 	"testing"
 
-	"go.etcd.io/etcd/clientv3"
+	clientv3 "go.etcd.io/etcd/client/v3"
 
 	"source.monogon.dev/metropolis/pkg/event/memory"
 )