Allow pg query param syntax

Allow configuring Postgres password through the socket URL.

For example:
```ruby
  ActiveRecord::DatabaseConfigurations::UrlConfig.new(
    :production, :production, 'postgres:///?user=user&password=secret&dbname=app', {}
  ).configuration_hash
```

will now return,

```ruby
  { :user=>"user", :password=>"secret", :dbname=>"app", :adapter=>"postgresql" }
```

activerecord/CHANGELOG.md

@@ -80,6 +80,23 @@
 
     *Kevin Newton*
 
+*   Allow configuring Postgres password through the socket URL.
+
+    For example:
+    ```ruby
+    ActiveRecord::DatabaseConfigurations::UrlConfig.new(
+      :production, :production, 'postgres:///?user=user&password=secret&dbname=app', {}
+    ).configuration_hash
+    ```
+
+    will now return,
+
+    ```ruby
+    { :user=>"user", :password=>"secret", :dbname=>"app", :adapter=>"postgresql" }
+    ```
+
+    *Abeid Ahmed*
+
 *   Fix `eager_loading?` when ordering with `Symbol`
 
     `eager_loading?` is triggered correctly when using `order` with symbols.

activerecord/lib/active_record/database_configurations/connection_url_resolver.rb

@@ -67,7 +67,7 @@ module ActiveRecord
               database: uri.opaque
             )
           else
-            query_hash.merge(
+            query_hash.reverse_merge(
               adapter: @adapter,
               username: uri.user,
               password: uri.password,

activerecord/test/cases/database_configurations/resolver_test.rb

@@ -62,6 +62,18 @@ module ActiveRecord
           }, pool_config.configuration_hash)
         end
 
+        def test_url_sub_key_merges_correctly_when_query_param
+          hash = { "url" => "abstract:///?user=user&password=passwd&dbname=app" }
+          pool_config = resolve_db_config :production, "production" => hash
+
+          assert_equal({
+            adapter:  "abstract",
+            user:     "user",
+            password: "passwd",
+            dbname:   "app"
+          }, pool_config.configuration_hash)
+        end
+
         def test_url_host_no_db
           pool_config = resolve_db_config "abstract://foo?encoding=utf8"
           assert_equal({