Manually assign entries for voting

[DesSnowy]

Description

This change allows admin to control when they wish to assign / reassign entries for voting. Existing submission for the assessment will be deleted if voting was previously assigned. This enables better control of when voting assignment can be done.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Code quality improvements

Changes to be made:

• Added new function reassign_voting to delete and reassign voting
• Added new call to reassign_voting in assessment_controller
• Added new function is_voting_assigned to check if voting is assigned for any of the questions in the assessment
• Added isVotingPublished field in assessment overview output

[DesSnowy]

Corresponding frontend PR: source-academy/frontend#2889

[coveralls]

coverage: 95.558% (+0.05%) from 95.508%
when pulling ef820f1 on DesSnowy:ControlOfInsertVoting
into 59fe997 on source-academy:master.

[RichDom2185]

LGTM, thanks a lot!