Make more objects lazy (#3403)

These `GithubObjects` can be retrieved lazily with `Github(…, lazy=True)`:
- AuthenticatedUser
- CheckRun
- CheckSuite
- Commit
- CommitComment
- Deployment
- Download
- Environment
- Gist
- GistComment
- GitRef
- GitRelease
- GitReleaseAsset
- Hook
- Issue
- IssueComment
- Label
- Milestone
- NamedUser
- Organization
- OrganizationSecret
- OrganizationVariable
- Project
- PullRequest
- PullRequestComment
- Repository
- RepositoryKey
- Secret
- Team
- Variable
- Workflow
- WorkflowRun