Use "immich-form-label" class for combobox label

[flesser]

On the "Edit date and time" dialog I noticed that the font sizes between the two input labels were different:

This PR changes the combobox label to use the existing immich-form-label CSS class instead of tailwind's text-sm:

The spacing is still off, but this may be fixed in a different PR (or in a later edit of this one).

As far as I can tell, the "Edit date and time" dialog is currently the only place where a combobox with visible label is used. In the settings pages, all the comboboxes have their label hidden.

(Kudos for having such a smooth and simple https://immich.app/docs/developer/setup/ which makes it really low-threshold to contribute! ❤️ )

[michelheusschen]

Thanks for the PR. The combobox is also used in the search bar where the label color changes slightly, but I don't think that's an issue:

Before

After

If you could also adjust the spacing of Date and Time to match, that would be great