[Bug]: End time of a silencing rule is not reflected in the edit dialog #1138

Bug description

When you edit an existing silencing rule with an end time, the end time is not reflected in the edit screen, but the duration is.

Expected behavior

Show the end time properly.

Steps to reproduce

1. Create a silencing rule with an end time
2. Find the new rule in the list
3. Note that it has a value in the end date column
4. Edit the rule
5. Notice that the end time is gone, but the duration is accurate.

Screenshots

Error Logs

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Desktop

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Additional context

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