Migrate pkg/authserver from logger shim to slog

[rdimitrov]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 75.49020% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.88%. Comparing base (ac495e6) to head (745d5d8).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/authserver/server/handlers/token.go	30.00%	7 Missing ⚠️
pkg/authserver/server/handlers/discovery.go	14.28%	6 Missing ⚠️
pkg/authserver/server/handlers/callback.go	61.53%	5 Missing ⚠️
pkg/authserver/server/handlers/dcr.go	40.00%	3 Missing ⚠️
pkg/authserver/server/handlers/authorize.go	50.00%	2 Missing ⚠️
pkg/authserver/storage/redis.go	66.66%	1 Missing ⚠️
pkg/authserver/upstream/oidc.go	87.50%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3880   +/-   ##
=======================================
  Coverage   66.88%   66.88%           
=======================================
  Files         444      444           
  Lines       44297    44297           
=======================================
+ Hits        29628    29629    +1     
+ Misses      12360    12358    -2     
- Partials     2309     2310    +1     

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