enh(NcDatetimePicker): convert lang computed value to prop

This allows to overwrite the locale configuration of the upstream date
picker library. Some apps (e.g. Calendar) overwrite some of the default
values which are specified here.

Signed-off-by: Richard Steinmetz <richard@steinmetz.cloud>

src/components/NcDatetimePicker/NcDatetimePicker.vue

@@ -128,7 +128,7 @@ export default {
 		:clearable="clearable"
 		:format="format ? format : formatTypeMap"
 		:formatter="formatter"
-		:lang="lang"
+		:lang="lang ? lang : defaultLang"
 		:minute-step="minuteStep"
 		:placeholder="placeholder ? placeholder : defaultPlaceholder"
 		:popup-class="{ 'show-week-number': showWeekNumber }"
@@ -237,6 +237,11 @@ export default {
 			default: null,
 		},
 
+		lang: {
+			type: Object,
+			default: null,
+		},
+
 		/**
 		 * The value to initialize, but also two-way bind the selected date. The date is – like the `Date` object in
 		 * JavaScript – tied to UTC. The selected time zone does not have an influence of the selected time and date
@@ -300,7 +305,7 @@ export default {
 		 *
 		 * @return {object}
 		 */
-		lang() {
+		defaultLang() {
 			return {
 				formatLocale: {
 					months: getMonthNames(),