[web] Add SVGs with arrows for sidebars modal

Summary: Add arrows exported from Figma design used in Sidebars Modal. Currently existing arrows for list of sidebars in chat list have different size and could not be easily used in the modal.

Test Plan:
Used the arrows in Sidebars Modal introduced in next diffs. They look as in designs.

Reviewers: tomek, atul

Reviewed By: tomek, atul

Subscribers: ashoat, adrian, abosh

Differential Revision: https://phab.comm.dev/D4607