[ERM-46] Update select/expand all functionality to display state properly

[ala-n]

User Story

As a Rollout Manager user, I want the "Select/Unselect All" functionality to behave consistently by default.

Scope

• Add a checkbox icon before the action text.
• Ensure the checkbox supports three states and reflects tree changes accordingly:
  1. Unselected – displayed when no items in the tree are selected.
     • Click → selects all items.
  2. Selected (regular checkmark) – displayed when all items are selected.
     • Click → unselects all items.
  3. Partially selected (filled square) – displayed when at least one, but not all, items are selected.
     • Click → selects all items.

Notes

• There is no need to change the control text after the checkbox icon is added.
• Always use static label: "Select all".