Mirroring use case fields (why pass through headers one doesn't understand.)

In Sarracenia, there is a use case involving pure directory mirroring. It means replicating a bit more file meta data. the wmo_mesh demonstration currently ignores these fields, and it is likely unnecessary for wmo usage. Documenting these fields as a demonstation that specific implementations may include fields that the general standard does not support, but both ends may use, but the intervening nodes should pass them unaltered.

The fields used to this:

* mtime - unix/linux modification time.

* atime - unix/linux access time

* mode - unix/linux traditional octal permission bits

The data replication works fine without any of these fields, but some end points may want to interpret them.

Start by locating the wmo_mesh demonstration and its existing documentation. Document mtime, atime, and mode as optional metadata that endpoints may interpret while intervening nodes pass them through unchanged, and make clear that replication works without them.

Written by the indexing model from the issue text.