On update clear field for the subsequent dropdowns

# Problem

There is a minor inconvenience during the drop-down selection for the course type, the exact course, and the slot for it. The issue is that every time a user selects, for example, a new subject, the slot for the same subject does not appear. The user needs to go and click on the X icon, then remove the slot, click on it again, and then select a new slot. Same goes for course tag also. For example if a person goes from foundation course to discipline course, the previous course and the search bar are still appearing where you have to click on the x icon again.

image 1 gives more visual clarity on the issue

## Image 1

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# Solution

I'd propose a simple solution is that when a user selects another input field for either the course or course type or the course itself, the subsequent drop-downs clear the input field and the user can just click on it again as if it was a fresh input.

So if a user goes from a formational code to a discipline code, the subsequent dropdown for the course type and the slot clear themselves and the user can select the new subject or the slot as needed.

Start by tracing the course type, exact course, and slot dropdowns described in the issue, reproducing the stale-selection flow shown in Image 1. Verify that changing an earlier selection clears each subsequent field and that the refreshed dropdowns can be selected without clicking the X icon.

索引モデルが issue の本文から書いたものです。