launch_manager daemon fails to link on glibc < 2.34 (missing -lrt for shm_open/shm_unlink)

## Description

`score/launch_manager/src/daemon/BUILD`'s `launch_manager` `cc_binary` only links
`-lpthread` on Linux. `process_group_manager.cpp` and
`details/process_launcher.cpp` both call `shm_open`/`shm_unlink`
(`score/launch_manager/src/daemon/src/process_group_manager/`), which live in
`librt` on glibc versions before 2.34 (glibc 2.34 folded `librt`'s symbols into
`libc` itself, so newer glibc happens to link fine either way, masking the
missing dependency).

On a glibc < 2.34 toolchain, linking `launch_manager` fails with undefined
references to `shm_open`/`shm_unlink`.

## Steps to reproduce

Build `//score/launch_manager/src/daemon:launch_manager` against a Linux glibc
target older than 2.34.

## Expected behavior

`launch_manager` links successfully regardless of the target's glibc version.

## Proposed fix

Add `-lrt` alongside `-lpthread` in the `cc_binary`'s Linux `linkopts`. Draft PR
incoming.