[FIX] project: set the default color in the project app

Description of the issue/feature this PR addresses:

-In the project module when the calendar view of a task is open click on any
  schedule, and popover is open.
-In popover tags colors are not visible

Current behavior before PR:
In the popover, tag field colors are not visible

Desired behavior after PR is merged:
tags colors are visible when opening the popover

Fix:
  we add options attribute in the many2many_tags widget.

task-3269548

closes odoo/odoo#120996

Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>