refactor(miniooni): divide et impera (#912)

This diff splits miniooni's implementation in smaller and more
easily tractable blocks ahead of future refactoring.

I'm trying to make `miniooni oonirun -i URL` as possible as
`miniooni -i URL oonirun`, because users typically expect this
kind of flexibity from modern Unix commands.

Part of https://github.com/ooni/probe/issues/2184

internal/cmd/miniooni/runx.go

@@ -0,0 +1,32 @@
+package main
+
+//
+// Run eXperiment by name
+//
+
+import (
+	"context"
+
+	"github.com/ooni/probe-cli/v3/internal/oonirun"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
+)
+
+// runx runs the given experiment by name
+func runx(ctx context.Context, sess oonirun.Session, experimentName string,
+	annotations map[string]string, extraOptions map[string]any, currentOptions Options) {
+	desc := &oonirun.Experiment{
+		Annotations:    annotations,
+		ExtraOptions:   extraOptions,
+		Inputs:         currentOptions.Inputs,
+		InputFilePaths: currentOptions.InputFilePaths,
+		MaxRuntime:     currentOptions.MaxRuntime,
+		Name:           experimentName,
+		NoCollector:    currentOptions.NoCollector,
+		NoJSON:         currentOptions.NoJSON,
+		Random:         currentOptions.Random,
+		ReportFile:     currentOptions.ReportFile,
+		Session:        sess,
+	}
+	err := desc.Run(ctx)
+	runtimex.PanicOnError(err, "cannot run experiment")
+}