Fix creating OAuth2 auth source from CLI

[daniil-pankratov]

This MR fixing creation OAuth2 auth source from CLI.
Problem is described here: #8356

[codecov-io]

Codecov Report

Merging #14116 (0497101) into master (4d22e24) will increase coverage by 0.00%.
The diff coverage is 18.75%.

@@           Coverage Diff           @@
##           master   #14116   +/-   ##
=======================================
  Coverage   42.34%   42.34%           
=======================================
  Files         726      726           
  Lines       77839    77852   +13     
=======================================
+ Hits        32960    32967    +7     
- Misses      39462    39469    +7     
+ Partials     5417     5416    -1     

Impacted Files	Coverage Δ
modules/auth/oauth2/oauth2.go	27.27% <0.00%> (-0.36%)	⬇️
routers/user/auth.go	11.97% <0.00%> (-0.08%)	⬇️
models/oauth2.go	34.14% <50.00%> (+0.81%)	⬆️
modules/git/tree_entry_nogogit.go	87.50% <0.00%> (-6.25%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️
models/error.go	38.98% <0.00%> (+0.48%)	⬆️
services/pull/pull.go	42.85% <0.00%> (+0.50%)	⬆️
modules/indexer/stats/db.go	48.00% <0.00%> (+8.00%)	⬆️
modules/indexer/stats/queue.go	76.47% <0.00%> (+11.76%)	⬆️

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[noerw]

Thanks for the PR! (fixes #8356 and #12938)

It would be nicer if goth providers were updated when adding a provider via CLI, instead of an error fallback during login.
The root of the issue is, that the CLI modifies the state of goth in the CLI process, not in the long-running gitea process.
Currently there is no RPC mechanism for this, we could add an API endpoint POST /api/v1/admin/auth-source for this.

As a first stopgap for the bug this still looks good to me.

[zeripath]

make lg-tm work