Plugin groups (#30320)

* add new pluginapi methods

* SAML login hook

* set ReAddRemovedMembers to true for plugin groups

* change to DoLogin signature for SAML

server/einterfaces/saml.go

@@ -4,6 +4,7 @@
 package einterfaces
 
 import (
+	saml2 "github.com/mattermost/gosaml2"
 	"github.com/mattermost/mattermost/server/public/model"
 	"github.com/mattermost/mattermost/server/public/shared/request"
 )
@@ -11,7 +12,7 @@ import (
 type SamlInterface interface {
 	ConfigureSP(c request.CTX) error
 	BuildRequest(c request.CTX, relayState string) (*model.SamlAuthRequest, *model.AppError)
-	DoLogin(c request.CTX, encodedXML string, relayState map[string]string) (*model.User, *model.AppError)
+	DoLogin(c request.CTX, encodedXML string, relayState map[string]string) (*model.User, *saml2.AssertionInfo, *model.AppError)
 	GetMetadata(c request.CTX) (string, *model.AppError)
 	CheckProviderAttributes(c request.CTX, SS *model.SamlSettings, ouser *model.User, patch *model.UserPatch) string
 }