XDG Support for wpscan db

[alichtman]

Fix #1586. This patch prefers the XDG path, and will only use the legacy path if it already exists on the machine. New installations will use XDG automatically, and doing the migration on your own is as simple as either:

$ mv ~/.wpscan $XDG_CACHE_HOME/wpscan

Demo

$ wpscan --update
_______________________________________________________________
         __          _______   _____
         \ \        / /  __ \ / ____|
          \ \  /\  / /| |__) | (___   ___  __ _ _ __ ®
           \ \/  \/ / |  ___/ \___ \ / __|/ _` | '_ \
            \  /\  /  | |     ____) | (__| (_| | | | |
             \/  \/   |_|    |_____/ \___|\__,_|_| |_|

         WordPress Security Scanner by the WPScan Team
                         Version 3.8.22
       Sponsored by Automattic - https://automattic.com/
       @_WPScan_, @ethicalhack3r, @erwan_lr, @firefart
_______________________________________________________________

[i] Updating the Database ...
[i] Update completed.


$ ls -l $XDG_CACHE_HOME/wpscan/*
.rw-rw-r-- alichtman alichtman  25 B  Fri Apr 28 2023 07:28:52 PM  .last_update
.rw-rw-r-- alichtman alichtman 2.4 KB Fri Apr 28 2023 07:28:15 PM  config_backups.txt
.rw-rw-r-- alichtman alichtman 1.1 KB Fri Apr 28 2023 07:28:16 PM  db_exports.txt
.rw-rw-r-- alichtman alichtman 3.1 MB Fri Apr 28 2023 07:28:16 PM  dynamic_finders.yml
.rw-rw-r-- alichtman alichtman 3.3 KB Fri Apr 28 2023 07:28:17 PM  LICENSE
.rw-rw-r-- alichtman alichtman  12 MB Fri Apr 28 2023 07:28:14 PM  metadata.json
.rw-rw-r-- alichtman alichtman  49 B  Fri Apr 28 2023 07:28:17 PM  sponsor.txt
.rw-rw-r-- alichtman alichtman 123 KB Fri Apr 28 2023 07:28:15 PM  timthumbs-v3.txt
.rw-rw-r-- alichtman alichtman 4.2 MB Fri Apr 28 2023 07:28:14 PM  wp_fingerprints.json

$ ls -l ~/.wpscan
lsd: /home/alichtman/.wpscan: No such file or directory (os error 2).

Licensing

By submitting code contributions to the WPScan development team via Github Pull Requests, or any other method, it is understood that the contributor is offering the WPScan company (company number 83421476900012), which is registered in France, the unlimited, non-exclusive right to reuse, modify, and relicense the code.

[alexsanford]

I've tested this and it seems to work well, except for one case noted below. @alichtman could you please test the case where the XDG_CACHE_HOME environment variable is not present, and make sure it works as expected?