[docs] Update nginx docs to use 127.0.0.1 instead of localhost

[tsmethurst]

Description

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This pull request updates our default nginx config documentation to resolve an issue with the default config refusing requests, to ensure others don't run into the same problem in future.

Basically, lots of these were appearing:

*459 connect() failed (111: Connection refused) while connecting to upstream

This change resolves it, see https://stackoverflow.com/a/52550758.

closes #1263

Checklist

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