docs(api-proxy): update code exmaple with explicit require (#21830)
docs(api-proxy): update code exmaple with explicit require (#21830)

* docs(api-proxy): update code exmaple with explicit require

http-proxy-middleware v1.0.0 introduces breaking change.
require/import of http-proxy-middleware is now explicit.

* docs(api-proxy): update code exmaples with explicit require

with comments that explains how to use the previous version

* chore: format

Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>

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