In the create collection coordinator documents we have strict as true, considering we have the create collection request parameters as fields in the document, after SERVER-62454 and SERVER-63732 we've added 3 new parameters to the request, making the coordinator document in new versions incompatible with old ones.

The crash scenario is the following: if we have a mixed binaries shard and a shard collection is issued against the primary node in 6.0 or 5.3 and then a stepdown happens, if the new primary is 5.0 then the parse of the document will fail, making the construction to throw, which in turn will hit the DDL coordinator construction invariant. We should set strict false in the create collection coordinator document.