Adds a couple of missing features for proper runtime configuration:
1. Favicon runtime configuration support via react-helmet
2. Placeholder values for APP_ID and MFE_CONFIG_API_URL in the sample
.env files
This handles a few things around the scheduled email UI. This includes:
1. Adding the schedule email UI date/time picker.
2. Adds states to the submit button for scheduling emails.
3. Drys out intl code and some submitting states.
4. Matches the email form UI to mocks.
This however does not include:
1. A table to show scheduled emails. Scheduled emails at the moment are
displayed in the "pending tasks" section.
2. Matching the tasks section to the mocks.
