Spotify: Add 502 error handling

[arsaboo]

Description

Continuation of the Spotify error handling improvements. I added 502 error handling. Without this, beets errors out:

Traceback (most recent call last):
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 182, in _handle_response
    response.raise_for_status()
  File "/home/arsaboo/.local/lib/python3.10/site-packages/requests/models.py", line 1021, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 502 Server Error: Bad Gateway for url: https://api.spotify.com/v1/tracks/XYZ

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/arsaboo/.local/bin/beet", line 8, in <module>
    sys.exit(main())
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beets/ui/__init__.py", line 1865, in main
    _raw_main(args)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beets/ui/__init__.py", line 1852, in _raw_main
    subcommand.func(lib, suboptions, subargs)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 482, in func
    self._fetch_info(items, ui.should_write(), opts.force_refetch)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 661, in _fetch_info
    popularity, isrc, ean, upc = self.track_info(spotify_track_id)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 682, in track_info
    track_data = self._handle_response(
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 221, in _handle_response
    raise SpotifyAPIError(
beetsplug.spotify.SpotifyAPIError: Spotify API error:
{
  "error" : {
    "status" : 502,
    "message" : "Bad gateway."
  }
}
URL:
https://api.spotify.com/v1/tracks/XYZ
params:
None

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[sampsyo]

Perfect; great that the "centralized" error handling here is paying off!