Disable administrative doorkeeper routes

[ThisIsMissEm]

These routes allow for the administration of OAuth 2.0 applications on the instance, however, they are not currently integrated into Mastodon, nor protected via the new user roles functionality, but instead by legacy admin flags.

I'll be the first to admit that the request specs added are not idiomatic necessarily, but they should be only temporary until we have a chance to properly integrate these routes into Mastodon. See #27478

@ClearlyClaire as requested.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (86500e3) 85.01% compared to head (b9e1dec) 85.01%.
Report is 61 commits behind head on main.

Files	Patch %	Lines
app/controllers/api/v1/statuses_controller.rb	87.50%	0 Missing and 1 partial ⚠️
app/controllers/auth/sessions_controller.rb	50.00%	0 Missing and 1 partial ⚠️
app/lib/signature_parser.rb	93.75%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #29187      +/-   ##
==========================================
- Coverage   85.01%   85.01%   -0.01%     
==========================================
  Files        1059     1060       +1     
  Lines       28277    28285       +8     
  Branches     4538     4537       -1     
==========================================
+ Hits        24040    24046       +6     
- Misses       3074     3075       +1     
- Partials     1163     1164       +1     

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[ThisIsMissEm]

Pretty sure codecov is misleading here, since the files it's saying there's missing coverage in are in files I've not touched?