feat: add simple username/password auth plugin

[DrmagicE]

No description provided.

[codecov-io]

Codecov Report

Merging #39 (6ed745a) into master (67c5578) will increase coverage by 1.29%.
The diff coverage is 64.01%.

@@            Coverage Diff             @@
##           master      #39      +/-   ##
==========================================
+ Coverage   36.75%   38.04%   +1.29%     
==========================================
  Files          51       55       +4     
  Lines        4416     4626     +210     
==========================================
+ Hits         1623     1760     +137     
- Misses       2540     2591      +51     
- Partials      253      275      +22     

Impacted Files	Coverage Δ
config/config.go	17.10% <ø> (ø)
plugin/admin/admin.go	2.40% <0.00%> (-0.03%)	⬇️
plugin/admin/config.go	0.00% <ø> (ø)
plugin/admin/utils.go	86.48% <ø> (ø)
server/server.go	4.82% <ø> (+<0.01%)	⬆️
plugin/auth/config.go	9.52% <9.52%> (ø)
plugin/auth/hooks.go	52.63% <52.63%> (ø)
plugin/auth/auth.go	71.08% <71.08%> (ø)
plugin/auth/grpc_handler.go	75.86% <75.86%> (ø)
... and 3 more

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