[MISC] Refactor and address most errcheck linter ignores

[nightah]

This is mostly a quality of life change.
When we first implemented the errcheck linter we ignored a number of items in our legacy codebase with intent to revisit down the track.

There's a only a few leftover TODO's, these have been left for the team to discuss on Matrix and agree on the way forward.

[authelia]

Artifacts

These changes are published for testing on Buildkite and DockerHub.

Docker Container

• docker pull authelia/authelia:misc-todo-cleanup

[codecov]

Codecov Report

Merging #1511 (9563cfd) into master (7c6a868) will decrease coverage by 0.45%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master    #1511      +/-   ##
==========================================
- Coverage   66.79%   66.34%   -0.46%     
==========================================
  Files         144      144              
  Lines        3981     4005      +24     
  Branches      169      169              
==========================================
- Hits         2659     2657       -2     
- Misses       1113     1129      +16     
- Partials      209      219      +10     

Flag	Coverage Δ
backend	66.68% <28.57%> (-0.71%)	⬇️
frontend	65.07% <ø> (+0.46%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/handlers/handler_register_u2f_step1.go	27.27% <0.00%> (-2.73%)	⬇️
internal/handlers/handler_register_u2f_step2.go	0.00% <0.00%> (ø)
internal/handlers/handler_configuration.go	81.81% <33.33%> (-18.19%)	⬇️
internal/handlers/handler_firstfactor.go	80.85% <33.33%> (-4.10%)	⬇️
internal/handlers/handler_register_totp.go	62.96% <33.33%> (-5.04%)	⬇️
internal/handlers/handler_reset_password_step1.go	68.42% <33.33%> (-8.05%)	⬇️
internal/handlers/handler_state.go	75.00% <33.33%> (-25.00%)	⬇️
internal/handlers/handler_user_info.go	86.88% <33.33%> (-2.95%)	⬇️
internal/handlers/response.go	71.42% <33.33%> (-13.36%)	⬇️
internal/middlewares/authelia_context.go	66.66% <0.00%> (-6.07%)	⬇️
... and 1 more

[james-d-elliott]

LGTM

[clems4ever]

Only a few comments but I'm ok for merging it like this since it already improves the situation a lot.