Improve support for Buttons in InputGroupAddon

[cagataycivici]

When used with a button inside, remove the default padding to take advantage of the borders of InputGroupAddon so we can do UIs like. Without the InputGroupAddon wrapper for buttons, we lose the borders that are synced with the Input.

<InputGroup>
   <Button label="Search" />
    <InputText placeholder="Keyword" />
</InputGroup>

<InputGroup>
    <InputText placeholder="Keyword" />
    <InputGroupAddon>
        <Button icon="pi pi-search" severity="secondary" variant="text" @click="toggle" />
    </InputGroupAddon>
</InputGroup>
<Menu ref="menu" :model="items" popup class="!min-w-fit" />

<InputGroup>
    <InputGroupAddon>
        <Button icon="pi pi-check" severity="secondary" />
    </InputGroupAddon>
    <InputText placeholder="Vote" />
    <InputGroupAddon>
        <Button icon="pi pi-times" severity="secondary" />
    </InputGroupAddon>
</InputGroup>