docs: redirect duplicate doc

[vinckr]

• fix: move oauth login flow description
• fix: redirect old doc and delete

as proposed moves the missing flow steps to the new oauth2 login doc, redirects and deletes the old doc.

closes #1389

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• 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 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 the necessary documentation within the code base (if appropriate).

Further comments

[aeneasr]

HTTP is so 1995 - please always use HTTPS :)

And follow the rules: https://github.com/ory/docs#placeholders-and-dummy-data

[vinckr]

AH right, thanks for keeping an eye out for this! Will see to keep our own styleguide more in mind 😁

[aeneasr]

pls resolve conflicts ty 🙏

[vinckr]

should be ready now @aeneasr