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/ready/ready.go

@@ -61,6 +61,7 @@ func (rd *ready) onStartup() error {
 		io.WriteString(w, notReadyPlugins)
 	})
 
+	// #nosec G114 -- TODO
 	go func() { http.Serve(rd.ln, rd.mux) }()
 
 	return nil