Support slash in file path in reduce command

[fabienheureux]

Reduce commands fails when using a nested xml file path

I am using a docker setup locally, and have my xml file located in /app/dump.xml in the docker container.
I am using the reduce command as : python manage.py reduce_xml /app/dump.xml
This causes the command to fail when writing the stats file as the command tries to write f = open(f"stats-{file_path}.json", "w") resulting in 'stats-/app/dump.xml.json'

Here is the full stacktrace

Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.8/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/base.py", line 330, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/base.py", line 371, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.8/site-packages/wagtail_wordpress_import/management/commands/reduce_xml.py", line 109, in handle
    f = open(f"stats-{file_path}.json", "w")
FileNotFoundError: [Errno 2] No such file or directory: 'stats-/app/dump.xml.json'

---

• Testing
  • CI passes
  • If necessary, tests are added for new or fixed behaviour
  • These changes do not reduce test coverage
• Documentation.
  • This PR adds or updates documentation
  • Documentation changes are not necessary because they do not change the reduce command behavior/arguments

[codecov-commenter]

Codecov Report

Merging #129 (a61b072) into main (3c27330) will increase coverage by 0.19%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   65.38%   65.57%   +0.18%     
==========================================
  Files          32       32              
  Lines        1251     1255       +4     
  Branches      222      222              
==========================================
+ Hits          818      823       +5     
+ Misses        392      391       -1     
  Partials       41       41              

Impacted Files	Coverage Δ
...wordpress_import/management/commands/reduce_xml.py	32.30% <83.33%> (+6.07%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3c27330...a61b072. Read the comment docs.

[nickmoreton]

@fabienheureux Thank you for the PR. The tests are now passing :)

[nickmoreton]

LGTM 👍