Check if plugin version matches running version (#17182)

Check if plugin version matches running version

When registering a plugin, we check if the request version matches the
self-reported version from the plugin. If these do not match, we log a
warning.

This uncovered a few missing pieces for getting the database version
code fully working.

We added an environment variable that helps us unit test the running
version behavior as well, but only for approle, postgresql, and consul
plugins.

Return 400 on plugin not found or version mismatch

Populate the running SHA256 of plugins in the mount and auth tables (#17217)

sdk/helper/pluginutil/multiplexing.go

@@ -2,6 +2,7 @@ package pluginutil
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -13,6 +14,8 @@ import (
 	"google.golang.org/grpc/status"
 )
 
+var ErrNoMultiplexingIDFound = errors.New("no multiplexing ID found")
+
 type PluginMultiplexingServerImpl struct {
 	UnimplementedPluginMultiplexingServer
 
@@ -62,7 +65,9 @@ func GetMultiplexIDFromContext(ctx context.Context) (string, error) {
 	}
 
 	multiplexIDs := md[MultiplexingCtxKey]
-	if len(multiplexIDs) != 1 {
+	if len(multiplexIDs) == 0 {
+		return "", ErrNoMultiplexingIDFound
+	} else if len(multiplexIDs) != 1 {
 		return "", fmt.Errorf("unexpected number of IDs in metadata: (%d)", len(multiplexIDs))
 	}