Add repository setting to enable/disable releases unit (#22671)

To go along with similar settings for issues, pulls, projects, packages.

services/forms/repo_form.go

@@ -146,6 +146,7 @@ type RepoSettingForm struct {
 	ExternalTrackerRegexpPattern          string
 	EnableCloseIssuesViaCommitInAnyBranch bool
 	EnableProjects                        bool
+	EnableReleases                        bool
 	EnablePackages                        bool
 	EnablePulls                           bool
 	EnableActions                         bool