[PULP-317] Allow configuring RPM repository layout to use a flat directory structure

[anfimovdm]

Is your feature request related to a problem? Please describe.
Currently, RPM repositories in pulp_rpm follow a specific directory structure where packages are organized under subdirectories based on their first letter. This format is:

<repo>/Packages/<first letter>/<package>.rpm

This structure makes us regenerate repodata each time after exporting packages from pulp.

Describe the solution you'd like
I propose adding a configurable option in the settings to allow users to choose a different repository layout. Specifically, the option would allow storing all RPM packages directly under the Packages/ directory instead of using the first-letter subdirectories.
Desired format:

<repo>/Packages/<package>.rpm

Describe alternatives you've considered

• Keeping the current structure as the default while introducing a configuration variable (e.g., FLAT_PACKAGE_LAYOUT=True) to enable the alternative format.