Introduce align_items parameter for ui.row, ui.column and ui.card

[falkoschindler]

Inspired by question #3174, this PR introduces a parameter to control how items are aligned within common layout elements. It is based on Tailwind's "Align Items" classes.

with ui.row(align_items='center'):
    ui.button('Button')
    ui.label('Label')

with ui.column(align_items='center'):
    ui.button('Button')
    ui.label('Label')

with ui.card(align_items='center'):
    ui.button('Button')
    ui.label('Label')

[rodja]

Ok. It's really quite common. But so are justify and content alignment. And what about gap, self-alignment, item placement and so on? We either add them step-by-step as parameters or give something like the LayoutBuilder another try.

[rodja]

Other relevant discussions might be #1806 and #117. Also the recently announced https://github.com/rio-labs/rio Python-UI framework has build it's own layout-mechanism which could be an inspiration.

[falkoschindler]

Yes, but because a complete layout system is still out of reach, I think we should improve NiceGUI's layouting options in smaller steps. I agree that gap would also be a useful parameter. But in contrast to the other alignments you mentioned, align_items is by far the one I use most frequently. Simply putting a label next to an input field or a button, you need to vertically center the row. But because we might add other parameters later, I chose the name align_items instead of just align or something.