Changes needed for MPA support - #555

Summary of Review & Applied Optimizations

I reviewed the changes in PR #555 and pushed a commit directly to add_mpa_examples with the following fixes and optimizations:

1. Restored google_ads_config.rb:

   • Reverted the accidental file rename of google_ads_config.rb to .template. google-ads-googleads.gemspec (line 29) explicitly lists google_ads_config.rb and build scripts expect this path.

2. Fixed Fatal Type Mismatch in update_user_access.rb:

   • ACCESS_ROLES is an array of strings (%w[ADMIN STANDARD READ_ONLY EMAIL_ONLY]), but update_user_access was passed a Symbol from the CLI (:ADMIN). This caused ACCESS_ROLES.include?(access_role) to always evaluate to false and raise an "Illegal access role specified" error.
   • Normalized and validated access_role = access_role.to_s.upcase.to_sym inside both update_user_access and invite_user_with_access_role.

3. Added Defensive Protobuf Traversal & Nil-Guards:

   • Added safe navigation (&.) on intermediate protobuf submessages in fetch_and_approve_pending_multi_party_auth_reviews.rb (access_review&.new_customer_user_access&.access_role, new_invite&.email_address, response.result_or_error&.first).
   • Safely guarded response.first&.customer_user_access in get_user_id to prevent NoMethodError if no record is returned.
   • Used safe navigation on response.result&.multi_party_auth_review and response.result&.resource_name.
   • Defaulted decoded partial failure errors to an empty array (failures || []).

4. In-Method Customer ID Sanitization:

   • Added customer_id = customer_id.to_s.tr('-', '') within fetch_and_approve_pending_multi_party_auth_reviews, fetch_pending_mpa_reviews, and approve_mpa_review so programmatic callers are protected regardless of input formatting.

5. Standardized CLI Error Reporting:

   • Updated the rescue Google::Ads::GoogleAds::Errors::GoogleAdsError => e blocks across all three examples to output e.request_id and structured error locations consistent with the client library's example suite.