### Apache Airflow version

2.4.1

### What happened

When there are large number of dag files, lets say 10K and each takes sometime to parse,  dag_parser doesnt pick any newly created files till all 10k files are finished parsing

`if not self._file_path_queue:
                self.emit_metrics()
                self.prepare_file_path_queue()`

Above logic only adds new files to queue when queue is empty

### What you think should happen instead

Every loop of dag processor should pick new files and add into file for parsing queue

### How to reproduce

_No response_

### Operating System

All

### Versions of Apache Airflow Providers

_No response_

### Deployment

Docker-Compose

### Deployment details

_No response_

### Anything else

_No response_

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

"""Information about single processing of one file"""
    num_dags: int
    import_errors: int
    last_finish_time: datetime | None
    last_duration: timedelta | None
    run_count: int
class DagParsingSignal(enum.Enum):
    """All signals sent to parser."""
    AGENT_RUN_ONCE = "agent_run_once"
    TERMINATE_MANAGER = "terminate_manager"
    END_MANAGER = "end_manager"
class DagFileProcessorAgent(LoggingMixin, MultiprocessingStartMethodMixin):
    """
    Agent for DAG file processing. It is responsible for all DAG parsing
    related jobs in scheduler process. Mainly it can spin up DagFileProcessorManager
    in a subprocess, collect DAG parsing results from it and communicate
    signal/DAG parsing stat with it.
    This class runs in the main `airflow scheduler` process.
    :param dag_directory: Directory where DAG definitions are kept. All
        files in file_paths should be under this directory
    :param max_runs: The number of times to parse and schedule each file. -1
        for unlimited.
    :param processor_timeout: How long to wait before timing out a DAG file processor
    :param dag_ids: if specified, only schedule tasks with these DAG IDs
    :param pickle_dags: whether to pickle DAGs.
    :param async_mode: Whether to start agent in async mode
    """
    def __init__(