Allow socket location customization via ENV

[Zaczero]

I want to store the data on an SMB share, but I am facing issues with the sockets (osm3s_v0.7.58_areas, osm3s_v0.7.58_osm_base) being inconveniently stored in the db directory. Ideally, db is stored on a share while sockets are stored in the local /run directory.

Error log:

File_Error Operation not permitted 1 /db/db//osm3s_v0.7.58_areas Unix_Socket::4
File_Error Operation not permitted 1 /db/db//osm3s_v0.7.58_osm_base Unix_Socket::4

[drolbr]

Implemented in ec0a668

Not yet released.