Explain how .zosattributes files can be used with Zowe CLI/Explorer

[adam-wolfe]

Is your request for enhancement related to a problem? Please describe.

The purpose/usage of .zosattributes files is not explained in existing documentation. The best explanation for how a .zosattributes file is supposed to work is in the webhelp here: https://docs.zowe.org/stable/web_help/index.html?p=zowe_zos-files_upload_dir-to-uss

...where it is described in a chunk of questionably formatted text at the very beginning of the (very long) command help for zowe files upload dtu -h.

Describe the solution you'd like

In Zowe Docs, we should explain:

1. What is the purpose of a .zosattributes file?
2. How do I create a .zosattributes file?
3. Where do I put a .zosattributes file?
4. Do .zosattributes files work with Zowe Explorer?

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Additional context