[Chapel Merge] Add foreach tech note

Branch: refs/heads/main
Revision: 0419a00
Author: e-kayrakli
Log Message:

Merge pull request #18386 from e-kayrakli/foreach-tech-note

Add foreach tech note

This PR adds a technote for the foreach loop added in #18046.

Under https://github.com/Cray/chapel-private/issues/2245 we were thinking
we can update the spec to include foreach, but we haven't made a lot of
improvements after the initial implementation that we wanted to. So, I'm adding
a tech note, instead.

make docs runs successfully and renders the doc nicely.

[Reviewed by @mppf]

Modified Files:
A doc/rst/technotes/foreach.rst

M doc/rst/technotes/index.rst

Compare: https://github.com/chapel-lang/chapel/compare/715bc67ff0f7...0419a0088770