refactor: replace hand-rolled SnakeYAML loader with Gestalt config

Replaces JettyConfigurationLoader (raw Map drilling, @SuppressWarnings)
with a typed Gestalt-based config pipeline:

- GitProxyConfig and nested POJOs (ServerConfig, DatabaseConfig,
  ProviderConfig, CommitSettings, FiltersConfig, WhitelistConfig) bind
  directly from YAML with no manual key lookups
- GitProxyConfigLoader merges: classpath base → optional local override
  → GITPROXY_* env var overrides (highest priority)
- JettyConfigurationBuilder now takes GitProxyConfig directly; all
  unchecked casts and helper getters removed
- Flat YAML structure: git-proxy: nesting removed so env var paths are
  clean (GITPROXY_SERVER_PORT, GITPROXY_DATABASE_TYPE, etc.)
- JettyConfigurationLoader and JettyConfigurationLoaderTest deleted
- src/test/resources/git-proxy-local.yml shadows the dev local config
  so unit tests see only base defaults
- CONFIGURATION.md rewritten to reflect new structure and env var table

Closes #8

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: coopernetes

build.gradle

@@ -38,6 +38,9 @@ ext {
     // YAML
     snakeyamlVersion = '2.2'
 
+    // Gestalt config
+    gestaltVersion = '0.37.2'
+
     // BouncyCastle
     bouncyCastleVersion = '1.83'
 

docker/git-proxy-local.yml

@@ -2,20 +2,19 @@
 # This file is mounted into the container at /app/conf/git-proxy-local.yml
 # and overrides the defaults in git-proxy.yml.
 
-git-proxy:
-  providers:
-    # Disable the default cloud providers; we only need the local Gitea instance.
-    github:
-      enabled: false
-    gitlab:
-      enabled: false
-    bitbucket:
-      enabled: false
+providers:
+  # Disable the default cloud providers; we only need the local Gitea instance.
+  github:
+    enabled: false
+  gitlab:
+    enabled: false
+  bitbucket:
+    enabled: false
 
-    # Local Gitea instance.
-    # Push (store-and-forward):  http://localhost:8080/push/gitea/<owner>/<repo>.git
-    # Proxy (transparent):       http://localhost:8080/proxy/gitea/<owner>/<repo>.git
-    gitea:
-      enabled: true
-      uri: http://gitea:3000
-      servlet-path: /gitea
+  # Local Gitea instance.
+  # Push (store-and-forward):  http://localhost:8080/push/gitea/<owner>/<repo>.git
+  # Proxy (transparent):       http://localhost:8080/proxy/gitea/<owner>/<repo>.git
+  gitea:
+    enabled: true
+    uri: http://gitea:3000
+    servlet-path: /gitea

docker/git-proxy-mongo.yml

@@ -6,15 +6,14 @@ database:
   url: mongodb://gitproxy:gitproxy@mongo:27017
   name: gitproxy
 
-git-proxy:
-  providers:
-    github:
-      enabled: false
-    gitlab:
-      enabled: false
-    bitbucket:
-      enabled: false
-    gitea:
-      enabled: true
-      uri: http://gitea:3000
-      servlet-path: /gitea
+providers:
+  github:
+    enabled: false
+  gitlab:
+    enabled: false
+  bitbucket:
+    enabled: false
+  gitea:
+    enabled: true
+    uri: http://gitea:3000
+    servlet-path: /gitea

docker/git-proxy-postgres.yml

@@ -16,15 +16,14 @@ database:
   username: gitproxy
   password: gitproxy
 
-git-proxy:
-  providers:
-    github:
-      enabled: false
-    gitlab:
-      enabled: false
-    bitbucket:
-      enabled: false
-    gitea:
-      enabled: true
-      uri: http://gitea:3000
-      servlet-path: /gitea
+providers:
+  github:
+    enabled: false
+  gitlab:
+    enabled: false
+  bitbucket:
+    enabled: false
+  gitea:
+    enabled: true
+    uri: http://gitea:3000
+    servlet-path: /gitea

jgit-proxy-dashboard/build.gradle

@@ -60,8 +60,8 @@ dependencies {
     runtimeOnly "org.postgresql:postgresql:${postgresVersion}"
     runtimeOnly "org.mongodb:mongodb-driver-sync:${mongoVersion}"
 
-    // YAML config
-    implementation "org.yaml:snakeyaml:${snakeyamlVersion}"
+    // Gestalt config (needed to catch GestaltException from GitProxyConfigLoader)
+    implementation "com.github.gestalt-config:gestalt-core:${gestaltVersion}"
 
     // Lombok
     compileOnly "org.projectlombok:lombok:${lombokVersion}"

jgit-proxy-dashboard/src/main/java/org/finos/gitproxy/dashboard/GitProxyWithDashboardApplication.java

@@ -14,8 +14,8 @@
 import org.finos.gitproxy.db.PushStore;
 import org.finos.gitproxy.git.LocalRepositoryCache;
 import org.finos.gitproxy.jetty.GitProxyServletRegistrar;
+import org.finos.gitproxy.jetty.config.GitProxyConfigLoader;
 import org.finos.gitproxy.jetty.config.JettyConfigurationBuilder;
-import org.finos.gitproxy.jetty.config.JettyConfigurationLoader;
 import org.finos.gitproxy.provider.GitProxyProvider;
 import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
 import org.springframework.web.servlet.DispatcherServlet;
@@ -38,8 +38,7 @@ public static void main(String[] args) throws Exception {
         log.info("Starting JGit Proxy with Dashboard...");
         writePidFile();
 
-        var configLoader = new JettyConfigurationLoader();
-        var configBuilder = new JettyConfigurationBuilder(configLoader);
+        var configBuilder = new JettyConfigurationBuilder(GitProxyConfigLoader.load());
 
         var threadPool = new QueuedThreadPool();
         threadPool.setName("jgit-proxy-dashboard");