feat: Add automation workflows (auto-assign, dependabot)

[aRustyDev]

Description

Add automation workflows from templates.hbs(github/workflows/automation) gist:

Files

• .github/workflows/auto-assign.yml - Auto-assigns owner to issues/PRs (single maintainer repos)
• .github/workflows/dependabot-issue.yml - Creates tracking issues for Dependabot PRs
• .github/dependabot.yml - Weekly GitHub Actions version updates

Source

Installed via:

gh gist clone eb3e040449ade0b0b0611b93cea454f2 gist-github-workflows-auto
INSTALL_DIR=. just --justfile gist-github-workflows-auto/github_workflows_auto.just install