fix(discord): Verify User Bot Installation Permission Take 2

[iamrajjoshi]

https://github.com/getsentry/sentry/pull/76360 broke prod, so trying again.

this time, we are just going to check if the user is actually part of the guild. to call this method, we needed to ask for guild info in the oauth scope.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.77419% with 1 line in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files	Patch %	Lines
src/sentry/integrations/discord/client.py	88.88%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #76586      +/-   ##
==========================================
+ Coverage   78.12%   78.18%   +0.05%     
==========================================
  Files        6856     6897      +41     
  Lines      306299   306733     +434     
  Branches    52741    52824      +83     
==========================================
+ Hits       239307   239807     +500     
+ Misses      60619    60538      -81     
- Partials     6373     6388      +15