chore(lint): enable gosec (#7792)

Enable "gosec" linter.

Exclude:

- All G115 (integer overflow) findings, to be fixed separately.

Add targeted gosec annotations for:

- non-crypto math/rand usage
- md5 used only for file change detection
- G114 ("net/http serve with no timeout settings"), to be fixed
  separately.

Other findings fixed.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/pprof/pprof.go

@@ -43,6 +43,7 @@ func (h *handler) Startup() error {
 	runtime.SetBlockProfileRate(h.rateBloc)
 
 	go func() {
+		// #nosec G114 -- TODO
 		http.Serve(h.ln, h.mux)
 	}()
 	return nil