Enable unparam linter (#31277)

Enable [unparam](https://github.com/mvdan/unparam) linter.

Often I could not tell the intention why param is unused, so I put
`//nolint` for those cases like webhook request creation functions never
using `ctx`.

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

.golangci.yml

@@ -22,6 +22,7 @@ linters:
     - typecheck
     - unconvert
     - unused
+    - unparam
     - wastedassign
 
 run: