fix: fixing schema type based on timestamps schema options value

[ark23CIS]

ignoring timestamps schema options field if createdAt, updatedAt fields are string, non-literal fields in TS.

Fix #14825

Summary
Currently, InferSchemaType and InferRawDocType incorrectly infer schema type based on timestamps schema options fields when the fields have a string type instead of string literal type. In order to avoid the incorrect users behavior mongoose will ignore the timestamp fields

[vkarpov15]

Thanks 👍