pirogue-screen-st7789-240x240: adjust package relationship for possible alternatives

[CyrilBrulebois]

The first version of the PiRogue hat requires this package.

Later on, we might have a second version pulling pirogue-screen-foo instead, a third one pulling pirogue-screen-bar, etc.

Since it's likely that all such packages are going to be trying to tweak DTB/DTBO/etc. on the SPI bus (or another one), it's probably a good idea to have all of them provide pirogue-screen, but also conflict against each other, to make sure there's only one installed at any given time. See Debian Policy for details.

We should make sure:

• We have all relevant fields in pirogue-screen-st7789-240x240.
• We have the following dependency in pirogue-base: pirogue-screen-st7789-240x240 | pirogue-screen.

Doing so means the package manager should install pirogue-screen-st7789-240x240 by default (which makes sense since that's the “current” version of the PiRogue hat), but would let users switch to a different pirogue-screen-* package later on.

Note: I wrote this bug report with pirogue-screen for the virtual package name, instead of the current pirogue-screen-controller. It's mostly because I thought that was the virtual package name, before checking the current value in debian/control before hitting the “Submit new issue” button. I don't have any strong feelings about the actual name, it would just happen to match the prefix that'd be common across all pirogue-screen-* packages.

[CyrilBrulebois]

Both packages updated. I think we should be good, but we'll have to check whether everything works fine for fresh Debian 12 installs, and when upgrading from Debian 11.