Refactor i18n Plugin Usage

[rak-phillip]

rancher/dashboard#10801 deprecates the existing method for installing the i18n plugin.

Where we would originally load the plugin via import:

// The plugin implicitly installs the plugin and extends Vue via the import
import '@shell/plugins/i18n';

We now explicitly install the plugin via Vue.use():

import i18n from '@shell/plugins/i18n';

// The plugin is explicitly loaded by the consumer, providing a Vue instance
Vue.use(i18n);