Function ParseGitHubUrl

Parses a GitHub repository URL into owner, repo, and an optional in-repo subpath.

Supports two forms:

• Single-app repo (the app's mj-app.json lives at the repo root): https://github.com/acme/mj-crm → { Owner: 'acme', Repo: 'mj-crm' }
• Multi-app repo (the app lives in a subdirectory — enables many apps per repo): https://github.com/MemberJunction/Integrations/CRM/HubSpot → { Owner: 'MemberJunction', Repo: 'Integrations', Subpath: 'CRM/HubSpot' }

Subpath is undefined for the single-app form, so existing callers that only read Owner/Repo are unaffected (fully backwards compatible).