Add modules/policy.nix with telemetry control option

[roberth]

Put users back in control.

Looking for your feedback.

[roberth]

I'll refer to this doc from places like https://flake.parts/best-practices-for-module-writing.html, but that's a different repo, flake.parts-website.

[drupol]

How about setting DO_NOT_TRACK env. variable ?

[roberth]

How about setting DO_NOT_TRACK env. variable ?

I gave it a brief mention as a recommendation.

devShells implementations should consider setting DO_NOT_TRACK=1 in their environment when false. See consoleDoNotTrack.com.

I'm not entirely certain that devShells should override this setting when it is set or unset at a user level, but it's certainly worth a shout-out.