Add tag for plugins supporting Qt6

[DelazJ]

I think I read something about this few weeks ago...
@rduivenvoorde @nyalldawson @troopa81 Is this OK?

[rduivenvoorde]

Yep looks good to me. I see in my plugin I use 'yes' instead of 'True', apparently both are valid?

[troopa81]

Looks good to me to!

[DelazJ]

I see in my plugin I use 'yes' instead of 'True', apparently both are valid?

No strong idea 😄 but I think there used to be this double usage of boolean in the plugin metadata file. No idea how I could verify this, but as most of the boolean tags in the sample here were using True/False I opted for consistency.

[rduivenvoorde]

FYI: I created an issue to add this tag to the plugins.xml: qgis/QGIS-Django#373

[elpaso]

@rduivenvoorde wouldn't be more future proof if we used minQtVersion/maxQtVersion (both defaulting to 5 for now) ?

[DelazJ]

So, verdict: supportsQt6 or minQtVersion/maxQtVersion?

[rduivenvoorde]

@DelazJ I like @elpaso 's proposal, though it would probably need some small changes in core then.
@nyalldawson do you have a strong opinion on this?

[DelazJ]

OK let's then close and wait for the min/max options. Might be a worth an issue report in code repo?