TW-5373 Add admin API SDK resources

[AaronDDM]

Summary

Updates the Ruby SDK admin/application API surface to match source-code truth for Applications, Redirect URIs, Manage Domains, Workspaces, Policies, Rules, and grant rule evaluations.

Changes

• Add Manage Domains resource for /v3/admin/domains CRUD, info, and verify.
• Add Workspaces resource for /v3/workspaces CRUD, auto_group, and manual_assign.
• Add Policies and Rules resources, including nested rules list unwrapping and rule evaluations.
• Add Applications#update for PATCH /v3/applications.
• Correct redirect URI update to PATCH.
• Update specs and CHANGELOG.

Jira

• https://nylas.atlassian.net/browse/TW-5373

Validation

• ruby -c over changed library files and specs
• bundle exec rspec ... could not run locally because the machine only has Ruby 2.6/Bundler 1.17.2; Gemfile.lock requires Bundler 2.7.2, which requires Ruby >= 3.2.0.
• Independent model verifier (codex exec, default gpt-5.5) PASS for endpoint/list-shape accuracy. Fable 5 CLI attempt was blocked by local Claude session limit, so Codex was used as the requested model-like verifier fallback.

[qasim-nylas]

LGTM 👍

[qasim-nylas]

LGTM 👍