feat: respect api_list_config exclusions in generate-updates

[torreypayne]

Exclude discoveryengine v1, v1alpha, and v1beta from automated generation until discovery doc issue is resolved.

📝 Exception Handling Logs

The following output demonstrates how these changes gracefully catch and report an anomalous Discovery configuration file (discoveryengine.v1 crash) across both explicit and automated batch flows:

1. Explicit CLI Execution (The requested flow)

$ bundle exec toys generate-updates discoveryengine:v1
[2026-08-07 18:41:45  INFO]  exec: ["bundle", "install"]
Bundle complete! 27 Gemfile dependencies, 94 gems now installed.
(1/1) Error when generating google-apis-discoveryengine_v1
Errors:
Failed generating google-apis-discoveryengine_v1 (exit code 1):
Discovery doc: https://raw.githubusercontent.com/googleapis/discovery-artifact-manager/master/discoveries/discoveryengine.v1.json
bundler: failed to load command: bin/generate-api (bin/generate-api)
/usr/local/google/home/torreypayne/google-api-ruby-client/google-apis-generator/lib/google/apis/generator/model.rb:46:in 'Google::Apis::DiscoveryV1::JsonSchema#qualified_name': undefined method 'qualified_name' for nil (NoMethodError)

          parent.qualified_name + '::' + generated_class_name
                ^^^^^^^^^^^^^^^

2. Automated CI Execution (The --all flow)

$ bundle exec toys generate-updates --all
Bundle complete! 27 Gemfile dependencies, 94 gems now installed.
(1/1) Error when generating google-apis-discoveryengine_v1
Errors:
Failed generating google-apis-discoveryengine_v1 (exit code 1):
Discovery doc: https://raw.githubusercontent.com/googleapis/discovery-artifact-manager/master/discoveries/discoveryengine.v1.json
bundler: failed to load command: bin/generate-api (bin/generate-api)
/usr/local/google/home/torreypayne/google-api-ruby-client/google-apis-generator/lib/google/apis/generator/model.rb:46:in 'Google::Apis::DiscoveryV1::JsonSchema#qualified_name': undefined method 'qualified_name' for nil (NoMethodError)

          parent.qualified_name + '::' + generated_class_name
                ^^^^^^^^^^^^^^^