feat: AGit push options starting with {base64} are decoded (#8479)

- When specifying push options, tooling like [git-repo-go](https://github.com/alibaba/git-repo-go) encodes pushoption values if they contain newlines or non-ASCII characters as they cannot be easily specified via the CLI otherwise.
- Recognize such base64 encoded values in the pushoptions (those that have the `{base64}` prefix), if the base64 decoding fails we return the original value.
- Resolves forgejo/forgejo#8161

<!--start release-notes-assistant-->

## Release notes
<!--URL:https://codeberg.org/forgejo/forgejo-->
- Features
  - [PR](https://codeberg.org/forgejo/forgejo/pulls/8479): <!--number 8479 --><!--line 0 --><!--description QUdpdCBwdXNoIG9wdGlvbnMgc3RhcnRpbmcgd2l0aCBge2Jhc2U2NH1gIGFyZSBkZWNvZGVk-->AGit push options starting with `{base64}` are decoded<!--description-->
<!--end release-notes-assistant-->

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8479
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

modules/git/pushoptions/pushoptions_test.go

@@ -4,6 +4,7 @@
 package pushoptions
 
 import (
+	"encoding/base64"
 	"fmt"
 	"testing"
 
@@ -92,6 +93,23 @@ func TestParse(t *testing.T) {
 		assert.False(t, options.Parse("unknown=value"))
 		assert.True(t, options.Empty())
 	})
+
+	t.Run("Base64 values", func(t *testing.T) {
+		options := New()
+
+		description := `I contain
+a
+line`
+		assert.True(t, options.Parse(fmt.Sprintf("%s={base64}%s", AgitDescription, base64.StdEncoding.EncodeToString([]byte(description)))))
+		val, ok := options.GetString(AgitDescription)
+		assert.True(t, ok)
+		assert.Equal(t, description, val)
+
+		assert.True(t, options.Parse(fmt.Sprintf("%s={base64}fooled you", AgitTitle)))
+		val, ok = options.GetString(AgitTitle)
+		assert.True(t, ok)
+		assert.Equal(t, "{base64}fooled you", val)
+	})
 }
 
 func TestReadEnv(t *testing.T) {