Feature request: Cell Metadata
In the ECMA spec ( https://www.ecma-international.org/publications-and-standards/standards/ecma-376/ ), we have this:

When writing some formulas using openpyxl 3.1 with `ArrayFormula`, it ends up as [CSE](https://exceljet.net/glossary/cse) formulas, which is sometimes what I want:

However, sometimes I just want this, while still using `ArrayFormula` (to prevent unwanted `@` from being added):

The difference in the XML is as follows:

The attribute `cm=1` probably refers to this bit in `metadata.xml`

In summary, I would like to somehow write this metadata using openpyxl, so that I can have array formulas without [CSE](https://exceljet.net/glossary/cse).
issue