sloproxy

feat(github): resolve GitHub token for release checks and asset updates master

- Add `util.ResolveGitHubToken` to resolve GitHub API tokens with priority order (`GITHUB_TOKEN`, `github_token`, and `GITSTORE_GIT_TOKEN` for GitHub repositories). - Set GitHub `Authorization` headers in management version check and asset updater requests when a token is resolved. Closes: #5189


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6 changed files