platform_manager: add DARWIN48V platform support (#260)

Summary:
# Description

Adds initial `platform_manager` support for `DARWIN48V` platform. Note that this depends on the changes in #257.

Pull Request resolved: #260

Test Plan:
FBOSS OSS build passes with CentOS 9 and Linux kernel 6.4.

Verified on DARWIN48V hardware.

The `platform_manager` service loads correctly:
```
# systemctl status platform_manager
● platform_manager.service - FBOSS Platform Manager
     Loaded: loaded (/etc/systemd/system/platform_manager.service; enabled; preset: disabled)
     Active: active (running) since Tue 2024-10-08 00:39:22 UTC; 1h 36min ago
    Process: 4744 ExecStartPre=/bin/bash -c [[ -f /opt/fboss/share/platform_configs/platform_manager.json ]] (code=exited, status=0/SUCCESS)
   Main PID: 4745 (platform_manage)

Reviewed By: kimdo8736

Differential Revision: D64087926

Pulled By: joancaneus

fbshipit-source-id: 93d72214d5fe06052b0b8c20546e670fb69b82f3

Author: adamcalabrigo