Update Gemfile and dependencies to use GitHub branches for react_on_rails and shakapacker

- Switch react_on_rails and shakapacker to use specific GitHub branches
- Update Gemfile.development_dependencies to reference GitHub repositories
- Update Gemfile.lock and spec/dummy files to reflect new gem sources
- Bump shakapacker version to 8.1.0 in package.json and yarn.lock
- Remove deprecated configuration option in react_on_rails initializer

Author: AbanoubGhadban

spec/dummy/package.json

@@ -63,7 +63,7 @@
     "sass": "^1.43.4",
     "sass-loader": "^12.3.0",
     "sass-resources-loader": "^2.0.0",
-    "shakapacker": "8.0.0",
+    "shakapacker": "8.1.0",
     "style-loader": "^3.3.1",
     "tailwindcss": "^3.2.7",
     "terser-webpack-plugin": "5",

spec/dummy/yarn.lock

@@ -5859,10 +5859,10 @@ sha.js@^2.4.0, sha.js@^2.4.8:
     inherits "^2.0.1"
     safe-buffer "^5.0.1"
 
-shakapacker@8.0.0:
-  version "8.0.0"
-  resolved "https://registry.yarnpkg.com/shakapacker/-/shakapacker-8.0.0.tgz#f29537c19078af7318758c92e7a1bca4cee96bdd"
-  integrity sha512-HCdpITzIKXzGEyUWQhKzPbpwwOsgTamaPH+0kXdhM59VQxZ3NWnT5cL3DlJdAT3sGsWCJskEl3eMkQlnh9DjhA==
+shakapacker@8.1.0:
+  version "8.1.0"
+  resolved "https://registry.yarnpkg.com/shakapacker/-/shakapacker-8.1.0.tgz#cb9f318f70cd59a99d3a46dda478aede657034c2"
+  integrity sha512-2OCl9KoKraW7CbUUfcEmTt/hK7IfOJx2h6LwsqEUUMsCcMWv3aFpZPjp5B74VdJxIqTgZo/8XVYKI0mj+itnxA==
   dependencies:
     js-yaml "^4.1.0"
     path-complete-extname "^1.0.0"