Support github refresh tokens

[anbraten]

closes #3804

Changes

• [x] add expiry when creating user
• [x] rename user.Token to AccessToken
• [x] rename user.Secret to RefreshToken
• [x] add support for github refresh tokens, ignore them if not provided as using an oauth app
• [x] add expiry to gitlab login (prevent direct refresh)

[woodpecker-bot]

Deployment of preview was successful: https://woodpecker-ci-woodpecker-pr-3811.surge.sh

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 25.21008% with 89 lines in your changes missing coverage. Please review.

Project coverage is 25.74%. Comparing base (fbb96ff) to head (a656070). Report is 3 commits behind head on main.

Files	Patch %	Lines
server/forge/github/github.go	5.40%	35 Missing :warning:
server/forge/gitlab/gitlab.go	21.05%	15 Missing :warning:
server/forge/forgejo/forgejo.go	42.10%	11 Missing :warning:
server/forge/gitea/gitea.go	42.10%	11 Missing :warning:
server/api/login.go	0.00%	7 Missing :warning:
server/forge/addon/args.go	0.00%	4 Missing :warning:
...r/forge/bitbucketdatacenter/bitbucketdatacenter.go	33.33%	2 Missing :warning:
server/forge/bitbucketdatacenter/convert.go	0.00%	2 Missing :warning:
server/forge/common/utils.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3811 +/- ## ========================================== + Coverage 25.73% 25.74% +0.01% ========================================== Files 366 366 Lines 27034 27008 -26 ========================================== - Hits 6956 6954 -2 + Misses 19538 19514 -24 Partials 540 540 ```

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