User subject type - handle deletion and multiple subject types of type User

[mahalakshme]

Steps to reproduce:

• Create some users in the org
• Create a subject type of type 'User'
• delete the subject type after the subjects for that user are created
• create another subject type of type 'User'
• sync
• the subject will not get synced

AC:

• The old subjects and user_subjects should get voided
• Independent of the above when an another subject type of type 'User' is created, again individuals for each user with different subject type should be created

Queries ran to fix the above issue: Link