feat: Added new flags to support release notes header and footer. (#1212)

* Added new flags to support release notes header and footer.

Created two flags for release generation.
--release-footer
--release-header
These flags can help you to add custom changelog text before/after changes that are generated by git log.

* Fix changelog.go to avoid lint errors

* Fix test typo

* Added tests for main, fixed bug with no passing options to release ctx

* Add @caarlos0  suggestions

main_test.go

@@ -11,7 +11,7 @@ import (
 	"github.com/goreleaser/goreleaser/pkg/config"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
-	yaml "gopkg.in/yaml.v2"
+	"gopkg.in/yaml.v2"
 )
 
 func init() {
@@ -107,6 +107,50 @@ func TestCustomReleaseNotesFile(t *testing.T) {
 	assert.NoError(t, releaseProject(params))
 }
 
+func TestCustomReleaseHeaderFileDontExist(t *testing.T) {
+	_, back := setup(t)
+	defer back()
+	params := testParams()
+	params.ReleaseHeader = "/header/that/dont/exist"
+	params.Snapshot = false
+	assert.Error(t, releaseProject(params))
+}
+
+func TestCustomReleaseHeaderFile(t *testing.T) {
+	_, back := setup(t)
+	defer back()
+	releaseHeader, err := ioutil.TempFile("", "")
+	assert.NoError(t, err)
+	createFile(t, releaseHeader.Name(), "some release header")
+	params := testParams()
+	params.ReleaseHeader = releaseHeader.Name()
+	params.Snapshot = false
+	params.SkipPublish = true
+	assert.NoError(t, releaseProject(params))
+}
+
+func TestCustomReleaseFooterFileDontExist(t *testing.T) {
+	_, back := setup(t)
+	defer back()
+	params := testParams()
+	params.ReleaseFooter = "/footer/that/dont/exist"
+	params.Snapshot = false
+	assert.Error(t, releaseProject(params))
+}
+
+func TestCustomReleaseFooterFile(t *testing.T) {
+	_, back := setup(t)
+	defer back()
+	releaseFooter, err := ioutil.TempFile("", "")
+	assert.NoError(t, err)
+	createFile(t, releaseFooter.Name(), "some release footer")
+	params := testParams()
+	params.ReleaseFooter = releaseFooter.Name()
+	params.Snapshot = false
+	params.SkipPublish = true
+	assert.NoError(t, releaseProject(params))
+}
+
 func TestBrokenPipe(t *testing.T) {
 	_, back := setup(t)
 	defer back()