redshift/gammastep: Unify common options

[thiagokokada]

Description

Nowadays services.{redshift,gammastep} modules are really similar. They should, since Gammastep is a fork of Redshift with the main objective is to support Wayland.

So instead of trying to maintain two separate modules, this commit unify the options in lib/options.nix file, while the implementation of the module itself ends up being really simple (just calling the common options with the necessary parameters to differentiate between them).

My reasoning for this is to make maintaining the modules easier, but also I want to update the modules to use config file instead of passing parameters via command-line, since this will allow it to support options not supported currently. Modifying both modules separately would be very error prone, so I decided to first unify them and afterwards I can open another PR migrating them to the config file.

Checklist

• Change is backwards compatible.

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[thiagokokada]

Did some improvements in tests so we make sure that this commit is not breaking anything.

[thiagokokada]

CC @rycee @petabyteboy .

[rycee]

Thanks! Merged to master.

I suspect that if gammastep supports both X and Wayland then we may want to consider removing the redshift module entirely but perhaps it's best to wait a while to see how the two projects develop.

In any case, thanks for the contribution!

[thiagokokada]

I suspect that if gammastep supports both X and Wayland then we may want to consider removing the redshift module entirely but perhaps it's best to wait a while to see how the two projects develop.

redshift seems to be focusing in having a dbus integration nowadays: jonls/redshift#54. gammastep itself doesn't seem to have much interested on it: https://gitlab.com/chinstrap/gammastep/-/issues/11. So yeah, the projects can diverge in the future, and some people may prefer to use one (for example, redshift for dbus support) or another (gammastep for wayland support).