### 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.
if not value:
            return value
        url_parts = urlsplit(value)
        netloc = None
        if url_parts.netloc:
            
            userinfo = None
            username = None
            password = None
            if "@" in url_parts.netloc:
                userinfo, _, host = url_parts.netloc.partition("@")
            else:
                host = url_parts.netloc
            if userinfo:
                if ":" in userinfo:
                    username, _, password = userinfo.partition(":")
                else:
                    username = userinfo
            
            username = self.process_username(username) if username else None
            password = "PASSWORD" if password else None
            
            if username and password and host:
                netloc = username + ":" + password + "@" + host
            elif username and host:
                netloc = username + "@" + host
            elif password and host:
                netloc = ":" + password + "@" + host
            elif host: