### Body

We had an issue where extra link class (`AIPlatformConsoleLink`) was removed in [PR](https://github.com/apache/airflow/pull/26836) without removing the class from the `provider.yaml` extra links this resulted in web server exception as shown in https://github.com/apache/airflow/pull/28449


**The Task:**
Add validation that classes of extra-links in provider.yaml are importable

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
git_version = self._get_version(["git", "--version"])
        ssh_version = self._get_version(["ssh", "-V"])
        kubectl_version = self._get_version(["kubectl", "version", "--short=True", "--client=True"])
        gcloud_version = self._get_version(["gcloud", "version"], grep=b"Google Cloud SDK")
        cloud_sql_proxy_version = self._get_version(["cloud_sql_proxy", "--version"])
        mysql_version = self._get_version(["mysql", "--version"])
        sqlite3_version = self._get_version(["sqlite3", "--version"])
        psql_version = self._get_version(["psql", "--version"])
        return [
            ("git", git_version),
            ("ssh", ssh_version),
            ("kubectl", kubectl_version),
            ("gcloud", gcloud_version),
            ("cloud_sql_proxy", cloud_sql_proxy_version),
            ("mysql", mysql_version),
            ("sqlite3", sqlite3_version),
            ("psql", psql_version),
        ]
    @property
    def _paths_info(self):