Add Gemfile to specify the gems to install and their version

Use cocoapods 1.11.x because I do not want to apply this workaround for
activesupport:
CocoaPods/CocoaPods#12081 (comment)

Gemfile

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+# The bare minimum for building, e.g. in Homebrew
+group :build do
+  gem 'rake', '~> 13.0'
+  gem 'xcpretty', '~> 0.3'
+end
+
+# In addition to :build, for contributing
+group :development do
+  gem 'cocoapods', '~> 1.11.0'
+end

Gemfile.lock

@@ -0,0 +1,103 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    CFPropertyList (3.0.6)
+      rexml
+    activesupport (6.1.7.6)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      i18n (>= 1.6, < 2)
+      minitest (>= 5.1)
+      tzinfo (~> 2.0)
+      zeitwerk (~> 2.3)
+    addressable (2.8.5)
+      public_suffix (>= 2.0.2, < 6.0)
+    algoliasearch (1.27.5)
+      httpclient (~> 2.8, >= 2.8.3)
+      json (>= 1.5.1)
+    atomos (0.1.3)
+    claide (1.1.0)
+    cocoapods (1.11.3)
+      addressable (~> 2.8)
+      claide (>= 1.0.2, < 2.0)
+      cocoapods-core (= 1.11.3)
+      cocoapods-deintegrate (>= 1.0.3, < 2.0)
+      cocoapods-downloader (>= 1.4.0, < 2.0)
+      cocoapods-plugins (>= 1.0.0, < 2.0)
+      cocoapods-search (>= 1.0.0, < 2.0)
+      cocoapods-trunk (>= 1.4.0, < 2.0)
+      cocoapods-try (>= 1.1.0, < 2.0)
+      colored2 (~> 3.1)
+      escape (~> 0.0.4)
+      fourflusher (>= 2.3.0, < 3.0)
+      gh_inspector (~> 1.0)
+      molinillo (~> 0.8.0)
+      nap (~> 1.0)
+      ruby-macho (>= 1.0, < 3.0)
+      xcodeproj (>= 1.21.0, < 2.0)
+    cocoapods-core (1.11.3)
+      activesupport (>= 5.0, < 7)
+      addressable (~> 2.8)
+      algoliasearch (~> 1.0)
+      concurrent-ruby (~> 1.1)
+      fuzzy_match (~> 2.0.4)
+      nap (~> 1.0)
+      netrc (~> 0.11)
+      public_suffix (~> 4.0)
+      typhoeus (~> 1.0)
+    cocoapods-deintegrate (1.0.5)
+    cocoapods-downloader (1.6.3)
+    cocoapods-plugins (1.0.0)
+      nap
+    cocoapods-search (1.0.1)
+    cocoapods-trunk (1.6.0)
+      nap (>= 0.8, < 2.0)
+      netrc (~> 0.11)
+    cocoapods-try (1.2.0)
+    colored2 (3.1.2)
+    concurrent-ruby (1.2.2)
+    escape (0.0.4)
+    ethon (0.16.0)
+      ffi (>= 1.15.0)
+    ffi (1.16.3)
+    fourflusher (2.3.1)
+    fuzzy_match (2.0.4)
+    gh_inspector (1.1.3)
+    httpclient (2.8.3)
+    i18n (1.14.1)
+      concurrent-ruby (~> 1.0)
+    json (2.6.3)
+    minitest (5.20.0)
+    molinillo (0.8.0)
+    nanaimo (0.3.0)
+    nap (1.1.0)
+    netrc (0.11.0)
+    public_suffix (4.0.7)
+    rake (13.0.6)
+    rexml (3.2.6)
+    rouge (2.0.7)
+    ruby-macho (2.5.1)
+    typhoeus (1.4.0)
+      ethon (>= 0.9.0)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
+    xcodeproj (1.23.0)
+      CFPropertyList (>= 2.3.3, < 4.0)
+      atomos (~> 0.1.3)
+      claide (>= 1.0.2, < 2.0)
+      colored2 (~> 3.1)
+      nanaimo (~> 0.3.0)
+      rexml (~> 3.2.4)
+    xcpretty (0.3.0)
+      rouge (~> 2.0.7)
+    zeitwerk (2.6.12)
+
+PLATFORMS
+  arm64-darwin-22
+
+DEPENDENCIES
+  cocoapods (~> 1.11.0)
+  rake (~> 13.0)
+  xcpretty (~> 0.3)
+
+BUNDLED WITH
+   2.2.33