MIT Climate - Add "ecosystems" subtopic

[shanbady]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/8926

Description (What does it do?)

This PR adds "ecosystems" as a subtopic of "Energy, Climate & Sustainability".

How can this be tested?

1. checkout main
2. manually run the mit climate task:

from learning_resources.tasks import get_mit_climate_data
get_mit_climate_data.apply()

3. you should see some output indicating that the "Ecosystems" topic was ignored/missing
4. checkout this branch
5. run data migrations via RUN_DATA_MIGRATIONS=true python manage.py migrate
6. restart celery
7. re-run the get_mit_climate_data and see that the output goes away
8. verify the new topic exists

[gumaerc]

👍 LGTM