[UX/UI] add squad icons

[lulcca]

Currently, there is no clear differentiation of squads on the sidebar, causing confusion.
What we think could help would be the addition of editable icons for the squad.

like this

We recommend creating it on figma.

• update squad creation modal (suggestion: with the icons as buttons)
• update squad edit modal (suggestion: with the icons as buttons and the current one highlighted)
• update sidebar with icons instead of numbers