Fixed incorrectly cleaning up python wheel dist folder (#1656)

## Changes
In https://github.com/databricks/cli/pull/1618 we introduced prepare
step in which Python wheel folder was cleaned. Now it was cleaned
everytime instead of only when there is a build command how it is used
to work.

This PR fixes it by only cleaning up dist folder when there is a build
command for wheels.

Fixes #1638 

## Tests
Added regression test

bundle/artifacts/whl/prepare.go

@@ -32,6 +32,11 @@ func (m *prepare) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostics
 		return diag.Errorf("artifact doesn't exist: %s", m.name)
 	}
 
+	// If there is no build command for the artifact, we don't need to cleanup the dist folder before
+	if artifact.BuildCommand == "" {
+		return nil
+	}
+
 	dir := artifact.Path
 
 	distPath := filepath.Join(dir, "dist")

bundle/tests/python_wheel/python_wheel_no_build/.gitignore

@@ -0,0 +1,3 @@
+build/
+*.egg-info
+.databricks

bundle/tests/python_wheel/python_wheel_no_build/bundle.yml

@@ -0,0 +1,16 @@
+bundle:
+  name: python-wheel
+
+resources:
+  jobs:
+    test_job:
+      name: "[${bundle.environment}] My Wheel Job"
+      tasks:
+        - task_key: TestTask
+          existing_cluster_id: "0717-132531-5opeqon1"
+          python_wheel_task:
+            package_name: "my_test_code"
+            entry_point: "run"
+          libraries:
+          - whl: ./dist/*.whl
+          - whl: ./dist/lib/my_test_code-0.0.1-py3-none-any.whl

bundle/tests/python_wheel_test.go

@@ -130,3 +130,16 @@ func TestPythonWheelBuildMultiple(t *testing.T) {
 	diags = bundle.Apply(ctx, b, match)
 	require.NoError(t, diags.Error())
 }
+
+func TestPythonWheelNoBuild(t *testing.T) {
+	ctx := context.Background()
+	b, err := bundle.Load(ctx, "./python_wheel/python_wheel_no_build")
+	require.NoError(t, err)
+
+	diags := bundle.Apply(ctx, b, bundle.Seq(phases.Load(), phases.Build()))
+	require.NoError(t, diags.Error())
+
+	match := libraries.ValidateLocalLibrariesExist()
+	diags = bundle.Apply(ctx, b, match)
+	require.NoError(t, diags.Error())
+}