Add Feed for Releases and Tags (#21696)

Fixes #19091

Add Feed for Releases and Tags, can be accessed through
`reponame/releases.rss`, `reponame/releases.atom`, `reponame/tags.rss`,
and `reponame/tags.atom`

Signed-off-by: Reo <reo_999@proton.me>

routers/web/feed/release.go

@@ -0,0 +1,50 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package feed
+
+import (
+	"time"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/context"
+
+	"github.com/gorilla/feeds"
+)
+
+// shows tags and/or releases on the repo as RSS / Atom feed
+func ShowReleaseFeed(ctx *context.Context, repo *repo_model.Repository, isReleasesOnly bool, formatType string) {
+	releases, err := repo_model.GetReleasesByRepoID(ctx, ctx.Repo.Repository.ID, repo_model.FindReleasesOptions{
+		IncludeTags: !isReleasesOnly,
+	})
+	if err != nil {
+		ctx.ServerError("GetReleasesByRepoID", err)
+		return
+	}
+
+	var title string
+	var link *feeds.Link
+
+	if isReleasesOnly {
+		title = ctx.Tr("repo.release.releases_for", repo.FullName())
+		link = &feeds.Link{Href: repo.HTMLURL() + "/release"}
+	} else {
+		title = ctx.Tr("repo.release.tags_for", repo.FullName())
+		link = &feeds.Link{Href: repo.HTMLURL() + "/tags"}
+	}
+
+	feed := &feeds.Feed{
+		Title:       title,
+		Link:        link,
+		Description: repo.Description,
+		Created:     time.Now(),
+	}
+
+	feed.Items, err = releasesToFeedItems(ctx, releases, isReleasesOnly)
+	if err != nil {
+		ctx.ServerError("releasesToFeedItems", err)
+		return
+	}
+
+	writeFeed(ctx, feed, formatType)
+}