feat: handle 'prompt' upstream parameter during OIDC flow

[David-Wobrock]

Documentation:

• https://openid.net/specs/openid-connect-core-1_0.html#AuthRequest
• https://developers.google.com/identity/openid-connect/openid-connect#prompt

Documentation added here: ory/docs#1410

Related issue(s)

Fixes #2709

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
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  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

[aeneasr]

Thank you! I reversed the order to ensure that prompt from user-provided values never overwrite prompt set by Kratos' business logic!

[David-Wobrock]

Thank you! I reversed the order to ensure that prompt from user-provided values never overwrite prompt set by Kratos' business logic!

Awesome! Thanks for that 🙇