fix(dev): allow passing mock country for geo-based redirects

[tinfoil-knight]

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Summary

Fixes #5051

The dev command doesn't allow a way for users to pass any flags to mock the current country to test out country based redirects which hinders local dev workflow.

Also, the "country" value used for redirects just defaults to US with no way to over-ride it which causes all requests for a route to be redirected in case a redirect rule with country value as US exists & prevents users from checking how the page without redirect looks.

This PR uses the value from pre-existing country flag for redirects. This allows the user to pass country values easily through the command line flag & test out country-based redirects properly.

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[github-actions]

📊 Benchmark results

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[tinfoil-knight]

Discussed w/ @kitop on Slack. Not sure why this fallback to 'us' exists but we decided to preserve it for backwards compatibility.

[tinfoil-knight]

@JWhist Just tagging you here since the country flag was originally added by you in #4708 for edge functions & I'm re-using it for redirects.

[lukasholzer]

Can we just simplify that instead of having a function for that?

Suggested change

	'x-country': cookieValues.nf_country || getCountry(geoCountry),
	'x-country': cookieValues.nf_country || geoCountry || 'us',

[tinfoil-knight]

@lukasholzer Made the suggested change.

[lukasholzer]

Thanks for your contribution but can we keep it simple? I think we don't need a function for that one