Added generic OAuth authentication support

[sinamics]

• Add new env variables to configure the oauth
• Show new oauth button if env is present.
• Update documentation

Notes!

• If user has registered to the application using credentails, we need to set the OAUTH_ALLOW_DANGEROUS_EMAIL_LINKING that will allow to merge the accounts.
• If user signin using oauth and then set`s a password from the user-settings, he will be able to login using both credentials and oauth.

Tested with Keycloak, Google, Github and Discord

Keycloak Configuration

ztnet:
  image: sinamics/ztnet:latest
  ...
  environment:
    OAUTH_ID=your-client-id
    OAUTH_SECRET=your-client-secret
    OAUTH_ALLOW_DANGEROUS_EMAIL_LINKING=true
    OAUTH_WELLKNOWN="http://{PROVIDER_URL}/auth/realms/{REALM}/.well-known/openid-configuration"

GitHub Configuration

ztnet:
  image: sinamics/ztnet:latest
  ...
  environment:
    OAUTH_ID=your-github-client-id
    OAUTH_SECRET=your-github-client-secret
    OAUTH_ACCESS_TOKEN_URL="https://github.com/login/oauth/access_token"
    OAUTH_AUTHORIZATION_URL="https://github.com/login/oauth/authorize"
    OAUTH_USER_INFO="https://api.github.com/user"
    OAUTH_SCOPE="read:user user:email"

Resolves #168