adding hcl tags so a terraform config can be generated

[janitha09]

package marshal

import (
	"fmt"

	"github.com/hashicorp/hcl2/gohcl"
	"github.com/hashicorp/hcl2/hclwrite"
	"github.com/signalsciences/go-sigsci"
)

type localCreateSignalTagBody sigsci.CreateSignalTagBody

func (l localCreateSignalTagBody) marshalSiteText(localName, site string) string {
	str := fmt.Sprintf(`resource %s "%s" {
	site_short_name = "%s"
`, l.TFSiteResourceName(), localName, site)
	f := hclwrite.NewEmptyFile()
	gohcl.EncodeIntoBody(&l, f.Body())
	str += string(f.Bytes())

	str += "}\n"
	return str
}```

a test for it looks like this
```go
func TestTextMarshalSiteSignalTag(t *testing.T) {
	createSignalTagBody := localCreateSignalTagBody{
		ShortName:   "Example Signal Tag 1",
		Description: "An example of a custom signal tag",
	}

	got := createSignalTagBody.marshalSiteText("test", "splunk-test")
	expected := "resource sigsci_site_signal_tag \"test\" {\n\tsite_short_name = \"splunk-test\"\nshort_name  = \"Example Signal Tag 1\"\ndescription = \"An example of a custom signal tag\"\n}\n"
	assert.Equal(t, expected, got)
}```