Ticketing Updates - Change client

[wrongecho]

This PR adds the ability to change a ticket's client

Additionally we're adding a new database field: ticket_source and will soon retire ticket_created_by.

• Ticket source will show where a ticket was raised from: an agent, the portal, via email, scheduled ticket, etc. Once this is implemented across the code base, we could also report on it to show the breakdown of where your tickets are raised (Feature Request: Ticket metric reporting #514).
• Ticket created by was originally designed when contacts were considered users. It quickly became clear that it was better to separate contacts and users, meaning there is now no way to differentiate whether the value in ticket_created_by is a user or contact. Given that we track a tickets assigned agent and client contact, and log all tickets raised, it seems safe to remove this field - for the sake of simplicity.

[wrongecho]

Test these changes at: https://ticketing0423656.pr-review.itflow.org
(automatic message)

[sonarcloud]

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2.2% Duplication