Mongoose 6.7.0发布

feat: upgrade to mongodb driver 4.11.0 #12446
feat: add UUID Schema Type (BSON Buffer SubType 4) #12268 #3208 hasezoey
feat(aggregation): add $fill pipeline stage #12545 raphael-papazikas
feat(types+schema): allow defining schema paths using mongoose.Types.* to work around TS type inference issues #12352
feat(schema): add alias() method that makes it easier to define multiple aliases for a given path #12368
feat(model): add mergeHooks option to Model.discriminator() to avoid duplicate hooks #12542
feat(document): add $timestamps() method to set timestamps for save(), bulkSave(), and insertMany() #12540