Conferences: add upcoming ones, some missing past ones

Upcoming: GolangConf 2026, GopherCamp 2026, GopherCon Singapore 2026,
GopherCon Africa 2026, GopherCon Israel 2026, GoLab

Past: TinyGo Conf 2025, Go Conference 2025, GopherCon Singapore 2025

Edit: added linebreak for Upcoming so it is under 73 characters.

Change-Id: I9fd1475fa23e1be5595485ffe2610f1d0815c5a8
GitHub-Last-Rev: 49b7e276bb12571c4ec046a1378eb92a811760e1
GitHub-Pull-Request: golang/wiki#89
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/745700
Reviewed-by: Sean Liao <sean@liao.dev>