Fix idle_checks field in grqphql to return the correct expire time in date format

## Motivation  

[Why is this Story important? Explain the context and reasons for this feature or change.]  

- Currently, the idle_checks returned by the `compute_session_node `query and `compute_session` query return the remaining time in seconds for the end of the session as remaining. This can cause inaccuracies due to the difference between when the server calculates and when the client receives it. Therefore, in order to fulfill the main purpose of the idle check, which is to show the exact end of the session, we need to return an absolute time as a date type.

## Required Features

[Clearly describe the features or functionality needed for this Story.]  

- Changed idle check gql response to return expired_date instead of remaining

## Impact  

[Specify which components or services will be affected by this Story.]  

-

## Testing Scenarios  

[Outline test cases or scenarios for validating the implementation.]  

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JIRA Issue: BA-592