feat: utilize IHttpClientFactory for improved HTTP client management

- Replaced direct `HttpClient` dependencies with `IHttpClientFactory` in `GithubService`, `ForgejoService`, and `ReleaseAssetDownloadService`.
- Added DI-configured HTTP client registrations for GitHub, Forgejo, and asset downloads in `Program.cs`.
- Consolidated HTTP client setup to enhance maintainability, configurability, and resource lifecycle management.

Services/GithubService.cs

@@ -6,16 +6,17 @@ using Microsoft.Extensions.Logging;
 
 namespace ForgejoReleaseSync.Services;
 
-public class GithubService(HttpClient httpClient, ILogger<GithubService> logger)
+public class GithubService(IHttpClientFactory httpClientFactory, ILogger<GithubService> logger)
 {
     public async Task<List<GithubReleaseResponseDto>> FetchRepoReleasesAsync(
         string owner, string repo, CancellationToken token = default)
     {
         try
         {
+            var httpClient = httpClientFactory.CreateClient("github");
+
             using var response = await httpClient.GetAsync(
-                new Uri($"https://api.github.com/repos/{owner}/{repo}/releases?per_page=3&page=1"),
-                token);
+                $"repos/{owner}/{repo}/releases?per_page=3&page=1", token);
             response.EnsureSuccessStatusCode();
 
             await using var stream = await response.Content.ReadAsStreamAsync(token);