use next_start_date when available in learning resource drawer

[gumaerc]

What are the relevant tickets?

Related to https://github.com/mitodl/hq/issues/8818

Description (What does it do?)

This PR updates the code in InfoItems, adjusting the start dates row. If the given resource has the next_start_date property populated, that date is used in place of the first chronological course run based on start_date.

How can this be tested?

• Spin up mit-learn on main
• Make sure you are configured properly to backpopulate xPRO courses
• Run docker compose exec web ./manage.py backpopulate_xpro_data
• After courses are backpopulated, visit search and look up "Principles of Biomanufacturing: Using Biotechnology to Manufacture Medicines"
• Once you see the course in the search results, click it to bring up the learning resource drawer
• Verify that the first start date shown under "Starts:" is different from the one on the card
• Switch to this branch (cg/drawer-start-date)
• Verify that the date in the drawer now matches the date on the card