### 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.
"""Anonymizer protocol."""
    def process_path(self, value) -> str:
        """Remove pii from paths."""
    def process_username(self, value) -> str:
        """Remove pii from username."""
    def process_url(self, value) -> str:
        """Remove pii from URL."""
class NullAnonymizer(Anonymizer):
    """Do nothing."""
    def _identity(self, value) -> str:
        return value
    process_path = process_username = process_url = _identity
    del _identity
class PiiAnonymizer(Anonymizer):
    """Remove personally identifiable info from path."""
    def __init__(self):
        home_path = os.path.expanduser("~")
        username = getuser()
        self._path_replacements = {home_path: "${HOME}", username: "${USER}"}
    def process_path(self, value) -> str:
        if not value:
            return value
        for src, target in self._path_replacements.items():
            value = value.replace(src, target)
        return value
    def process_username(self, value) -> str:
        if not value:
            return value
        return value[0] + "..." + value[-1]
    def process_url(self, value) -> str: