meson: Manage lockfile paths for all daemons through the build system

[rdmark]

The build system currently has logic to detect or configure the path to the netatalk lockfile (PID file).

However, atalkd/papd also use lockfiles, whose paths are defined via logic in include/atalk/paths.h

These should be consolidated as Meson logic.

[rdmark]

The logic is in this section https://github.com/Netatalk/netatalk/blob/ef5601c57747d7cea22f8957a029b4b80502d455/meson.build#L1797

Rather than pointing to a specific file, I think the lockfile variable to be defined as the directory that contains the lockfiles. Then, leave it up to the deamon logic to put their named lockfile in said dir.