Fix #18211: Validation of video start and end time in creator dashboard

[yungmulah]

Overview

1. This PR fixes #[18211].
2. This PR does the following: Implementation of front end validation of start and end times of videos in the creator dashboard. Allows users to only submit videos if start time < end time or else error will be raised. Handles special case where both start and end time are 0 and allows to submit for playing the whole video. Also update back-end validation to ensure consistency.

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Proof that changes are correct

275773719-456747d6-c3b0-4a31-91f9-4fc0a201572a.mov

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[oppiabot]

Assigning @vojtechjelinek for the first pass review of this PR. Thanks!

[yungmulah]

PTAL @seanlip

[seanlip]

Thanks, I'm adding @kevintab95 and @vojtechjelinek who can review this.

[vojtechjelinek]

Thanks! Backend changes look good to me. I've added a few frontend comments. Please try to fix them, but deffering to @kevintab95 to check if they are fixed correctly.

[vojtechjelinek]

It is a bit weird that the name of the function is called validateVideoStartEnd but the true return value means this is an invalid video

[yungmulah]

Thanks, I agree and changed the function name to isVideoStartTimeValid that returns true if the start time < end time. PTAL @kevintab95.