chore: revise workflows and documentation

[burigolucas]

Description

This PR improves the fork contributor CI experience by introducing a two-tier workflow architecture and automating the full CI setup for forks.

Two-tier CI for PRs

• Adds a new Tier 1 ansible-lint.yml workflow that runs on all PRs (including forks) without requiring secrets or maintainer approval. It uses a new .ansible-lint-ci config that mocks private Red Hat collection modules and roles (redhat.openshift.k8s, ansible.controller.*, etc.), enabling lint feedback immediately for external contributors.
• Tier 2 (full CI with AUTOMATION_HUB_TOKEN) continues to require maintainer approval for fork PRs, as before.
• pre-commit.yml now explicitly skips the ansible-lint hook (SKIP=ansible-lint) to avoid duplication with the dedicated Tier 1 workflow.

Fork CI (ci-fork.yml)

• New workflow that lets fork contributors run the complete test suite (full ansible-lint, sanity tests, integration tests) directly in their fork before opening a PR upstream — no waiting for maintainer approval.
• Requires only AUTOMATION_HUB_TOKEN configured as a fork repository secret.
• Includes a sync-tags job that automatically creates the latest upstream version tag in the fork on every push. This satisfies the changelog-lint job's version resolution requirement without any manual steps. The tag is pointed at the fork's default branch HEAD to avoid the GITHUB_TOKEN workflow OAuth scope restriction.

Trigger and workflow revisions

• pre-commit.yml now also triggers on push to non-main/v2 branches so fork contributors get pre-commit feedback before opening a PR.
• gitleaks.yml trigger broadened to run on all pushes (not just main/v2).
• Concurrency groups added to pr-title-validation.yml, pre-commit.yml, ansible-lint.yml, and gitleaks.yml to cancel superseded runs.
• All workflows upgraded to actions/checkout@v6.

Other

• Pins tox>=4.15.1,<4.28 in test-requirements.txt to avoid a regression in tox 4.28+ that rejects env names like py313-2.18 (interprets the collection version as a Python version).
• Updates the PR description template (.github/pull_request_template.md).
• Updates CONTRIBUTING.md with a full explanation of the two-tier CI architecture and a step-by-step fork CI setup guide.

Type of Change

• feat: A new feature
• fix: A bug fix
• docs: Documentation changes
• style: Formatting, missing semi colons, etc; no code change
• refactor: Refactoring production code
• test: Adding missing tests, refactoring tests; no production code change
• chore: Updating configs, etc; no production code change

Pull Request Title

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Example: feat: add role

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