Add read_channel_content permission (#24118)

* Add read_channel_content permission

* fix tests

* update system console default permissions per role

* add read_channel_content to e2e defaultRolesPermissions

* Migration to include custom roles

* change deprecated isNotExactRole for isNotRole

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/app_test.go

@@ -112,6 +112,7 @@ func TestDoAdvancedPermissionsMigration(t *testing.T) {
 	expected1 := map[string][]string{
 		"channel_user": {
 			model.PermissionReadChannel.Id,
+			model.PermissionReadChannelContent.Id,
 			model.PermissionAddReaction.Id,
 			model.PermissionRemoveReaction.Id,
 			model.PermissionManagePublicChannelMembers.Id,