fix(cli): print plugin downloading status to stderr (#2269)

Printing the status to stdout causes problems when piping the results of
a query command to another bazel command.

---

### Type of change

- Bug fix (change which fixes an issue)

**For changes visible to end-users**

- Suggested release notes are provided below:

Aspect CLI plugin downloading status line is now printed to stderr.

### Test plan

- Manual testing; please provide instructions so we can reproduce:

Pipe a cli query call to another bazel command.

For example,

first clear any bazelisk / aspect cli caches
```
$ rm -rf ~/Library/Caches/aspect
$ rm -rf ~/Library/Caches/aspect-cli
$ rm -rf ~/Library/Caches/bazelisk
```

then pipe a bazel query into a bazel build
```
$ /Users/greg/aspect/silo/bazel-bin/cli/core/cmd/aspect/aspect_/aspect build $(/Users/greg/aspect/silo/bazel-bin/cli/core/cmd/aspect/aspect_/aspect query //somepath/...)
2023/05/26 17:05:41 Downloading https://releases.bazel.build/6.1.1/release/bazel-6.1.1-darwin-x86_64...
Downloading https://github.com/aspect-build/plugin-fix-visibility/releases/download/v0.1.0/fix-visibility-darwin_amd64...
Downloading https://static.aspect.build/aspect/5.1.10/plugin-aspect-workflows-darwin_amd64...
Downloading https://static.aspect.build/aspect/5.1.10/plugin-aspect-workflows-darwin_amd64.sha256...
Downloading https://github.com/aspect-build/plugin-fix-visibility/releases/download/v0.1.0/fix-visibility-darwin_amd64.sha256...
Loading: 0 packages loaded
Loading: 0 packages loaded
INFO: Analyzed N targets (0 packages loaded, 0 targets configured).
INFO: Found N targets...
Target //somepath:foobar up-to-date:
  bazel-bin/somepath/foobar
INFO: Elapsed time: 0.305s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```
GitOrigin-RevId: aa6993e581ff6e9e75da82dae485866919862a92

Author: gregmagolan

pkg/plugin/client/download.go

@@ -108,7 +108,7 @@ func downloadFile(originURL, destDir, destFile string, mode fs.FileMode) (string
 		defer os.Remove(tmpfile.Name())
 		defer tmpfile.Close()
 
-		faint.Println("Downloading", originURL)
+		faint.Fprintf(os.Stderr, "Downloading %s...\n", originURL)
 
 		resp, err := http.Get(originURL)
 		if err != nil {