Refactor unix domain socket store config (#11109)

Following what is outlined in #10766 refactor the uds-remote-store such
that the member variables (state) don't live in the store itself but in
the config object.

Additionally, the config object includes a new necessary constructor
that takes a scheme & authority.

Tests are commented out because of linking errors with the current config system.
When there is a new config system we can reenable them.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>

src/libstore/local-fs-store.hh

@@ -11,6 +11,15 @@ struct LocalFSStoreConfig : virtual StoreConfig
 {
     using StoreConfig::StoreConfig;
 
+    /**
+     * Used to override the `root` settings. Can't be done via modifying
+     * `params` reliably because this parameter is unused except for
+     * passing to base class constructors.
+     *
+     * @todo Make this less error-prone with new store settings system.
+     */
+    LocalFSStoreConfig(PathView path, const Params & params);
+
     const OptionalPathSetting rootDir{this, std::nullopt,
         "root",
         "Directory prefixed to all other paths."};