[as2_map_server] Align header file names with class names

### Feature Description

To ensure code consistency and readability across the project, we should follow this convention:

- Header files containing a class should be named exactly like the class they define.

For example, in `as2_map_server`, we currently have a `plugin_base.hpp` file that defines the `MapServerBase` class.
This file should be renamed to `map_server_base.hpp `to avoid duplicated file names across the framework and to align with the naming convention.

### Implementation Considerations

_No response_