Plugins: Tighten requirements for multiplexing (#17403)

Change the multiplexing key to use all `PluginRunner` config (converted to a struct which is comparable), so that plugins with the same name but different env, args, types, versions etc are not incorrectly multiplexed together.

Co-authored-by: Christopher Swenson <christopher.swenson@hashicorp.com>

sdk/plugin/mock/backend.go

@@ -2,11 +2,14 @@ package mock
 
 import (
 	"context"
+	"os"
 
 	"github.com/hashicorp/vault/sdk/framework"
 	"github.com/hashicorp/vault/sdk/logical"
 )
 
+const MockPluginVersionEnv = "TESTING_MOCK_VAULT_PLUGIN_VERSION"
+
 // New returns a new backend as an interface. This func
 // is only necessary for builtin backend plugins.
 func New() (interface{}, error) {
@@ -60,6 +63,9 @@ func Backend() *backend {
 	}
 	b.internal = "bar"
 	b.RunningVersion = "v0.0.0+mock"
+	if version := os.Getenv(MockPluginVersionEnv); version != "" {
+		b.RunningVersion = version
+	}
 	return &b
 }