Add `clients/ruby` scaffolding

clients/ruby/.gitignore

+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+/*.gem
+
+# rspec failure tracking
+.rspec_status

clients/ruby/.rspec

+--format documentation
+--color
+--require spec_helper

clients/ruby/.rubocop.yml

+AllCops:
+  TargetRubyVersion: 2.6
+
+Style/StringLiterals:
+  Enabled: true
+  EnforcedStyle: double_quotes
+
+Style/StringLiteralsInInterpolation:
+  Enabled: true
+  EnforcedStyle: double_quotes
+
+Layout/LineLength:
+  Max: 120

clients/ruby/Gemfile

+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+# Specify your gem's dependencies in ruby.gemspec
+gemspec
+
+gem "rake", "~> 13.0"
+gem "rspec", "~> 3.0"
+gem "rubocop", "~> 1.21"

clients/ruby/Gemfile.lock

+PATH
+  remote: .
+  specs:
+    gitlab-global-service-client-poc (0.1)
+      grpc
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ast (2.4.2)
+    diff-lcs (1.5.1)
+    google-protobuf (3.25.3-aarch64-linux)
+    googleapis-common-protos-types (1.12.0)
+      google-protobuf (~> 3.18)
+    grpc (1.61.0-aarch64-linux)
+      google-protobuf (~> 3.25)
+      googleapis-common-protos-types (~> 1.0)
+    json (2.7.1)
+    language_server-protocol (3.17.0.3)
+    parallel (1.24.0)
+    parser (3.3.0.5)
+      ast (~> 2.4.1)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.0)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.0)
+    rubocop (1.60.2)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.30.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    unicode-display_width (2.5.0)
+
+PLATFORMS
+  aarch64-linux
+
+DEPENDENCIES
+  gitlab-global-service-client-poc!
+  rake (~> 13.0)
+  rspec (~> 3.0)
+  rubocop (~> 1.21)
+
+BUNDLED WITH
+   2.4.4

clients/ruby/gitlab-topology-service-client.gemspec

+# frozen_string_literal: true
+
+require_relative 'lib/gitlab/cells/topology_service/version'
+
+required_files = [
+]
+
+unless required_files.all? { |file| File.exist?(file) }
+  raise "Some required files are missing: #{required_files}"
+end
+
+Gem::Specification.new do |spec|
+  spec.name = "gitlab-global-service-client-poc"
+  spec.version = Gitlab::Cells::TopologyService::VERSION
+  spec.authors = ["Kamil Trzciński"]
+  spec.email = ["ayufan@ayufan.eu"]
+
+  spec.summary = "Client library to interact with Topology Service for GitLab Cells architecture"
+  spec.homepage = "https://gitlab.com/gitlab-org/cells/topology-service"
+  spec.license = "MIT"
+  spec.required_ruby_version = ">= 2.6.0"
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  spec.files = Dir.chdir(__dir__) do
+    `git ls-files -z`.split("\x0").reject do |f|
+      (f == __FILE__) || f.match(%r{\A(?:(?:bin|test|spec|features)/|\.(?:git|circleci)|appveyor)})
+    end
+  end
+  spec.require_paths = ["lib"]
+
+  spec.add_dependency "grpc"
+end

clients/ruby/lib/gitlab/cells/topology_service.rb

+# frozen_string_literal: true
+
+require_relative 'topology_service/version'

clients/ruby/lib/gitlab/cells/topology_service/version.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Cells
+    module TopologyService
+      VERSION = '0.1'
+    end
+  end
+end

clients/ruby/spec/spec_helper.rb

+# frozen_string_literal: true
+
+require 'rspec'
+require 'gitlab/cells/topology_service'
+
+RSpec.configure do |config|
+  # Enable flags like --only-failures and --next-failure
+  config.example_status_persistence_file_path = ".rspec_status"
+
+  # Disable RSpec exposing methods globally on `Module` and `main`
+  config.disable_monkey_patching!
+
+  config.expect_with :rspec do |c|
+    c.syntax = :expect
+  end
+end