feat: multiple assigned users

[xdissidia]

This will enable assigning of multiple users to a task

includes functions in
dashboard, tasks and activities

this removes the all functions using assigned_to_user_id in tasks table
and converted to many-to-many relationship to task_user table

dependents

migrations of

2025_04_14_132049_create_task_user_table

and seeder to migrate existing users to multiple assigned users

MigrateTaskAssignedToUserIdToAssignedUsers

[vstruhar]

Hi, thanks for the PR!
Will review it later, but will also have to think about if assigning multiple users to a task is needed.
Since in JIRA, Asana, Linear... etc, task can be assigned to single user only.

[jtphelan]

Teamwork allows multiple users on a project. We used it to assign a dev and QA on the same task so they could go back and forth on it.