Add PR title validation for Training operator repository using reusable workflow

### Context

Ensuring PR titles (and merge commits) always follow a defined naming convention is necessary to maintain a clean and readable repository.

Ref: https://github.com/canonical/bundle-kubeflow/issues/1376

### What needs to get done

1. Add new action, possibly named on_pull_request_lint_title, which uses the reusable workflow defined [here](https://github.com/canonical/charmed-kubeflow-workflows/blob/main/.github/workflows/_pull-request-lint-title.yaml)

### Definition of Done

1. Action runs when a PR is created, updated, reopened or synchronized
2. PR title validation is working

Start by inspecting the repository's existing files under .github/workflows and the reusable workflow at charmed-kubeflow-workflows/.github/workflows/_pull-request-lint-title.yaml. Add the PR title validation action with the requested pull request events, then verify that the workflow invokes the reusable workflow and validates PR titles.

Written by the indexing model from the issue text.