feat: oidc provider epic games

[Jorgagu]

Implementation of Epic Games OpenID Connect.

https://dev.epicgames.com/docs/web-api-ref/authentication

https://api.epicgames.dev/epic/oauth/v1/.well-known/openid-configuration

It's almost work with provider generic but the token endpoint need the client id and client secret in Authorization basic header.

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Attention: 34 lines in your changes are missing coverage. Please review.

Comparison is base (67360cf) 78.33% compared to head (5233571) 78.17%.
Report is 5 commits behind head on master.

❗ Current head 5233571 differs from pull request most recent head 483da7e. Consider uploading reports for the commit 483da7e to get more accurate results

Files	Patch %	Lines
selfservice/strategy/oidc/provider_epic_games.go	0.00%	34 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3449      +/-   ##
==========================================
- Coverage   78.33%   78.17%   -0.16%     
==========================================
  Files         347      347              
  Lines       23804    23671     -133     
==========================================
- Hits        18646    18505     -141     
- Misses       3749     3765      +16     
+ Partials     1409     1401       -8     

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