Improve NuGet API Parity (#21291) (#34940)

Fixes #21291, allowing icons and other missing attributes to appear for
NuGet packages from inside Visual Studio like they do with GitHub Nuget
packages.

Adds additional NuGet package information, particularly `IconURL`, to
bring the Gitea NuGet API more in-line with GitHub's NuGet API.

ref: https://learn.microsoft.com/en-us/nuget/api/search-query-service-resource

models/packages/package_version.go

@@ -37,6 +37,14 @@ type PackageVersion struct {
 	DownloadCount int64              `xorm:"NOT NULL DEFAULT 0"`
 }
 
+// IsPrerelease checks if the version is a prerelease version according to semantic versioning
+func (pv *PackageVersion) IsPrerelease() bool {
+	if pv == nil || pv.Version == "" {
+		return false
+	}
+	return strings.Contains(pv.Version, "-")
+}
+
 // GetOrInsertVersion inserts a version. If the same version exist already ErrDuplicatePackageVersion is returned
 func GetOrInsertVersion(ctx context.Context, pv *PackageVersion) (*PackageVersion, error) {
 	e := db.GetEngine(ctx)