Change format of iteration dates

What does this MR do and why?

Omit start year and sometimes due year depending on whether or not the two dates share the same year and whether or not that year is the current year.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Scenario: start and due date are both in the current year

Click to expand

Place seen	Before	After
Project iteration cadences page
Project iteration cadence
Issue sidebar
Project issue board (and sidebar)
Group iteration cadences page
Group iteration cadence
Group iteration cadence edit (unchanged)
Group issue board (and sidebar)

Scenario: start and due date are both in a year that is not the current year (e.g., both next year)

Click to expand

Place seen	Before	After
Project iteration cadences page
Project iteration cadence
Issue sidebar
Project issue board (and sidebar)
Group iteration cadences page
Group iteration cadence
Group iteration cadence edit (unchanged)
Group issue board (and sidebar)

Scenario: start and due dates are not in the same year (e.g., start this year and end next year)

Click to expand

Place seen	Before	After
Project iteration cadences page (specific item unchanged, see Dec 14, 2024 - Jan 10, 2025)
Project iteration cadence (Unchanged)
Issue sidebar (Unchanged)
Project issue board (and sidebar) (Unchanged)
Group iteration cadences page (Specific item unchanged, see Dec 14, 2024 - Jan 10, 2025)
Group iteration cadence (Unchanged)
Group iteration cadence edit (unchanged)
Group issue board (and sidebar) (Unchanged)

How to set up and validate locally

1. Check out this branch
2. Visit a group in the GDK
3. Create a new iteration cadence that is configured so that there will be iterations during the current year and next year
   1. The start date, duration of each iteration and number of future iterations to plan can be edited, so set this values in such a way that there is at least 1 iteration that is fully within the current year, one that starts in the current year and ends next year, and at least one that is fully in the next year
4. Go to a project within the group and visit the issues board
5. Pick an issue at random that has no iteration and assign it to an iteration that is completely within the current year from the iteration cadence created ins step 3
6. Pick an issue at random that has no iteration and assign it to the iteration that starts in the current year and ends next year from the iteration cadence created ins step 3
7. Pick an issue at random that has no iteration and assign it to an iteration that is completely within the next year from the iteration cadence created ins step 3
8. You will see that:
   1. The issue with an iteration that is completely within the current year does not have any years on its start and due dates
   2. The issue that is in the iteration that spans the current and next years has years for both the start and due dates
   3. The issue with an iteration that is completely within next year has a year shown only for the due date, not the start date
9. Visit each of the three issues
10. You will see that steps 8.1 through 8.3 are also true of the iteration information shown on the issue sidebar on each issue page
11. Click through to each of the three iterations
12. you will see that:
    1. The iteration that is completely within the current has a year shown only for the due date, not the start date
    2. The iteration that spans the current and next years has years for both the start and due dates
    3. The iteration that is completely within next year has a year shown only for the due date, not the start date
13. Visit the project iterations list
14. Scroll to the iteration cadence you created and expand it
15. you will see that:
    1. The iteration that is completely within the current year has a year shown only for the due date, not the start date
    2. The iteration that spans the current and next years has years for both the start and due dates
    3. The iteration that is completely within next year has a year shown only for the due date, not the start date

Related to #454580 (closed)

Closes #344619 (closed)