CleanupDefunctSiloEntries broken for MultipleMembershipCollection

We are using MongoDBMembershipStrategy.Muiltiple and noticed that we have a large number of defunct entries accumulating in the membership table which aren't getting cleaned-up as expected.

I believe this is related to DateTime vs. DateTimeOffset issues in the DeleteManyAsync call.

Orleans.Providers.MongoDB/Orleans.Providers.MongoDB/Membership/Store/Multiple/MultipleMembershipCollection.cs

Lines 177 to 180 in 22bc56b

    
           public Task CleanupDefunctSiloEntries(string deploymentId, DateTimeOffset beforeDate) 
        
           { 
        
               return Collection.DeleteManyAsync(x => x.DeploymentId == deploymentId && x.Status == (int)SiloStatus.Dead && x.Timestamp < beforeDate); 
        
           }

x.Timestamp is a DateTime while beforeDate is a DateTimeOffset. The comparison between the two results in an implicit conversion to DateTimeOffset and a query filter like this being generated:

{{ "DeploymentId" : "My-Deployment-Id", "Status" : 6, "Timestamp" : { "$lt" : [NumberLong("637852876860000000"), 0] } }}

Zero results will be returned by this query because the DateTimeOffset is being converted to an array which cannot be compared against the date-formatted Timestamp field.

	public Task CleanupDefunctSiloEntries(string deploymentId, DateTimeOffset beforeDate)
	{
	return Collection.DeleteManyAsync(x => x.DeploymentId == deploymentId && x.Status == (int)SiloStatus.Dead && x.Timestamp < beforeDate);
	}