fix(collectors): execute Erasmus Mundus check on startup

feat(collectors): add Erasmus Mundus collector

feat(collectors): add Campus France collector

feat(collectors): add Campus France collector

fix(collector): prevent empty AU results from blocking API startup

feat(collectors): add African Union opportunities collector

feat(collectors): add University of Bamenda collector

feat(collectors): add University of Dschang collector

feat(collectors): add University of Douala opportunity collector

feat(collectors): add University of Buea opportunity collector

feat(collectors): add MINESUP collector validation

feat(collectors): add MINESUP collector validation

feat(opportunities): add official UNESCO internships collector

fix(opportunities): improve Mastercard Foundation collector

feat(collectors): implement Mastercard Foundation collector

feat: add Chevening opportunity collector