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>

tests/unit/libstore/uds-remote-store.cc

@@ -0,0 +1,23 @@
+// FIXME: Odd failures for templates that are causing the PR to break
+// for now with discussion with @Ericson2314 to comment out.
+#if 0
+#  include <gtest/gtest.h>
+
+#  include "uds-remote-store.hh"
+
+namespace nix {
+
+TEST(UDSRemoteStore, constructConfig)
+{
+    UDSRemoteStoreConfig config{"unix", "/tmp/socket", {}};
+
+    EXPECT_EQ(config.path, "/tmp/socket");
+}
+
+TEST(UDSRemoteStore, constructConfigWrongScheme)
+{
+    EXPECT_THROW(UDSRemoteStoreConfig("http", "/tmp/socket", {}), UsageError);
+}
+
+} // namespace nix
+#endif