Initialize run.Configs in the NewSTEP functions [#67]

This fixes the run package's leaky abstraction; other packages no longer
need to know or care that run.Config even exists.

Note that since the various Steps now depend on having a non-nil pointer
to a run.Config, it's unsafe (or at least risky) to initialize them
directly. They should be created with their NewSTEPNAME functions. All
their fields are now private, to reflect this.

internal/run/config_test.go

@@ -0,0 +1,35 @@
+package run
+
+import (
+	"github.com/pelotech/drone-helm3/internal/env"
+	"github.com/stretchr/testify/suite"
+	"strings"
+	"testing"
+)
+
+type ConfigTestSuite struct {
+	suite.Suite
+}
+
+func TestConfigTestSuite(t *testing.T) {
+	suite.Run(t, new(ConfigTestSuite))
+}
+
+func (suite *ConfigTestSuite) TestNewConfig() {
+	stdout := &strings.Builder{}
+	stderr := &strings.Builder{}
+	envCfg := env.Config{
+		Namespace: "private",
+		Debug:     true,
+		Stdout:    stdout,
+		Stderr:    stderr,
+	}
+	cfg := newConfig(envCfg)
+	suite.Require().NotNil(cfg)
+	suite.Equal(&config{
+		namespace: "private",
+		debug:     true,
+		stdout:    stdout,
+		stderr:    stderr,
+	}, cfg)
+}