Added duration field to Activity and create/update endpoints

[ShalevKk]

Description

Added new field to Activity entity - duration. Each course needs a duration so that the engine would assign it exactly this number of hours.

Related Issues

Closes bgu-nasa/main#44

Changes Made

• Added Duration in Activity Domain entity
• Modified Activity service create and update methods to get also duration param
• Modified requests/response objects and the activity mapper to contain duration
• Modified create/update activity endpoints in SubjectController to use the duration field

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing completed
• All existing tests pass

Checklist

• My code follows the project's code style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Database Changes

• No database changes
• Database migration included
• Database migration instructions provided below

Configuration Changes

• No configuration changes required
• Configuration changes documented below

[noamarg]

Looks good