Malformed iCal code when saving a Schedule by Day

Description

When a Schedule runs Monthly and recurs on the First [Day of Week] of the month, the iCal code that is being generated is missing a '1' in front of the day of the week code. For this schedule:

It is set to run on the 1st Tuesday of the month, but the malformed iCal code is registering as "The Tuesday of every month"

When we preview the iCal code & upcoming dates, we see the schedule is calculating on EVERY Tuesday, not just the 1st

When the iCal code is being generated for the 1st day-of-week monthly occurrence, it is missing the 1 before TU RRULE:FREQ=MONTHLY;BYDAY=TU and should be outputting RRULE:FREQ=MONTHLY;BYDAY=1TU

Actual Behavior

When the iCal code is being generated for the 1st day-of-week monthly occurrence, it is outputting RRULE:FREQ=MONTHLY;BYDAY=TU which is causing occurrences to be calculated for EVERY Tuesday, and is rendering in the Schedule description as "The Tuesday of every month"

Expected Behavior

When iCal code is generated for the 1st day-of-week monthly occurrence, I would expect it to output RRULE:FREQ=MONTHLY;BYDAY=1TU which would calculate only first-Tuesday-of-the-month occurrences, and would render in the Schedule description as "The 1st Tuesday of every month"

Steps to Reproduce

Go to Admin Tools->Checkin->Schedules and create a new Schedule
Click Edit Schedule
Select Recurring, Monthly, The [First] day of [any weekday] (2nd, 3rd, 4th, 5th, and Last all work correctly)
Save the schedule and new Schedule.
See that the description does not include '1st [weekday]'
Edit the Schedule and click Preview to see that the occurrences are every week on the selected weekday.

Issue Confirmation

[X] Perform a search on the Github Issues to see if your bug or enhancement is already reported.
[X] Reproduced the problem on a fresh install or on the demo site.

Rock Version

16.2 (Demo site), 16.4

Client Culture Setting

en-US

SparkDevNetwork / Rock