client: add configurable doublezerod socket

[linuskendall]

Summary of Changes

• Added a command line flag to the doublezero client binary to specify the socket file
• The doublezerod server binary allows the placement of the socket file in any location, but the client binary was hardcoded to use /var/run/doublezerod/doublezerod.sock.
• In environments such as immutable hosts /var/run/doublezerod may be awkward to use or unavailable
• Is a CHANGELOG.md update needed? Possibly, it's a very minor change

Testing Verification

• Run on a doublezero host; ./doublezero --sock-file /var/lib/.../4b2b7d84-c521-3eae-d33b-e7bc1534cd3c/alloc/doublezerod.sock status

[juan-malbeclabs]

Closing this in favor of the new PR: #3634