Allow custom indicators to be placed to the left

### Problem

Currently new indicators seems only allowed to the right

devs may want to offer alternative menus, not for indicating state, but for apps or files
or think a specific custom indicator may offer a placement to the user

it also feels very unbalanced for people who like clutter, with all the clutter only to the right
Let us do our own bad UI choices !

### Proposal

indicator property to center either right or left - but not leave them to be leftmost or rightmost either

### Prior Art (Optional)

_No response_