Add support for multiple OIDC providers

[ShuP1]

Current Behavior

Alpine configuration supports only a single OIDC provider using ALPINE_OIDC_* variables.

Proposed Behavior

For exemple, allowing login from both Gitlab and Github OIDC providers.

• Support multiple oidc providers in Alpine: Add support for multiple OIDC providers stevespringett/Alpine#448
  • Rename variables to ALPINE_OIDC_<name>_* like APLINE_OIDC_GITLAB_ISSUER=https://gitlab.com
• In OpenID Connect Groups => Teams mapping, add provider name
  • (Provider: gitlab + Group: inkscape) gives access to Team Inkscape dev

Checklist

• I have read and understand the contributing guidelines
• I have checked the existing issues for whether this enhancement was already requested