feat(Table): allow columns class customization

Resolves #366

docs/content/4.data/1.table.md

@@ -72,6 +72,7 @@ Use the `columns` prop to configure which columns to display. It's an array of o
 - `key` - The field to display from the row data.
 - `sortable` - Whether the column is sortable. Defaults to `false`.
 - `direction` - The sort direction to use on first click. Defaults to `asc`.
+- `class` - The class to apply to the column cells.
 
 ::component-example{class="grid"}
 ---

src/runtime/components/data/Table.vue

@@ -7,7 +7,7 @@
             <UCheckbox :checked="indeterminate || selected.length === rows.length" :indeterminate="indeterminate" @change="selected = $event.target.checked ? rows : []" />
           </th>
 
-          <th v-for="(column, index) in columns" :key="index" scope="col" :class="[ui.th.base, ui.th.padding, ui.th.color, ui.th.font, ui.th.size]">
+          <th v-for="(column, index) in columns" :key="index" scope="col" :class="[ui.th.base, ui.th.padding, ui.th.color, ui.th.font, ui.th.size, column.class]">
             <slot :name="`${column.key}-header`" :column="column" :sort="sort" :on-sort="onSort">
               <UButton
                 v-if="column.sortable"
@@ -96,7 +96,7 @@ export default defineComponent({
       default: () => []
     },
     columns: {
-      type: Array as PropType<{ key: string, sortable?: boolean, [key: string]: any }[]>,
+      type: Array as PropType<{ key: string, sortable?: boolean, class?: string, [key: string]: any }[]>,
       default: null
     },
     columnAttribute: {