[BITV] Special buttons color contrast improvements

[nimishavijay]

As discussed in #4193 the color contrast of the special buttons (success, warning, error buttons) is not sufficient.

So the new color codes we could use are:
--color-error: #E71F18
--color-success: #328544

This would also affect other components using these colors such as NcNoteCard.
@nextcloud/designers agree that all occurrences of the warning button can be replaced by either error or secondary button. Hence the warning color can remain unchanged.

cc @JuliaKirschenheuter @marcoambrosini @AndyScherzinger

[AndyScherzinger]

Looks good to me, great choice of tone, easier on the eyes (on bright displays I think) 👍

[szaimen]

Looks good 👍