Introduce event owner user role

[shreyanshdwivedi]

Is your feature request related to a problem? Please describe.

Currently, owners of the event cannot be differentiated. So organizer event role is to be changed to owner, to differentiate and make it clear.

Additional context

On it.
Reference fossasia/open-event-frontend#3012 (comment)

[shreyanshdwivedi]

@iamareebjamal @mariobehling should I change the role organizer to owner or add a new role as owner?

[shreyanshdwivedi]

As discussed on call, I'll be adding a new role owner and keep other roles as it is