[#84154564] .env-sample points to local IHAT_URL

This will give us more useful error messages if iHat is not running,
where using ihat.example.com difficult to diagnose errors further down
the line.

— RW DT
Merge pull request #714 from Tahi-project/env-sample-fox

[#84154564] .env-sample points to local IHAT_URL