Add 3 Digit World Cup 2025 tournament and listing

[shdewz]

Also updates index page to include other instalments (previously only included 2021)

Self-check

• The changes are tested against the contribution checklist

[osu-wiki-observatory]

Someone else has edited same files as you did. Please check their changes in case they conflict with yours:

• Add Resurrection Cup 2024 tournament and listing. #12582, files:
  • wiki/Tournaments/en.md

[osu-wiki-observatory]

Someone else has edited same files as you did. Please check their changes in case they conflict with yours:

• Add ANZT6W tournament page #12616, files:
  • wiki/Tournaments/en.md