chore(login): migrate nextjs login to monorepo (#10134)

# Which Problems Are Solved

We move the login code to the zitadel repo.

# How the Problems Are Solved

The login repo is added to ./login as a git subtree pulled from the
dockerize-ci branch.
Apart from the login code, this PR contains the changes from #10116

# Additional Context

- Closes https://github.com/zitadel/typescript/issues/474
- Also merges #10116  
- Merging is blocked by failing check because of:
- https://github.com/zitadel/zitadel/pull/10134#issuecomment-3012086106

---------

Co-authored-by: Max Peintner <[email protected]>
Co-authored-by: Max Peintner <[email protected]>
Co-authored-by: Florian Forster <[email protected]>

login/.github/pull_request_template.md

@@ -0,0 +1,13 @@
+### Definition of Ready
+
+- [ ] I am happy with the code
+- [ ] Short description of the feature/issue is added in the pr description
+- [ ] PR is linked to the corresponding user story
+- [ ] Acceptance criteria are met
+- [ ] All open todos and follow ups are defined in a new ticket and justified
+- [ ] Deviations from the acceptance criteria and design are agreed with the PO and documented.
+- [ ] Vitest unit tests ensure that components produce expected outputs on different inputs.
+- [ ] Cypress integration tests ensure that login app pages work as expected on good and bad user inputs, ZITADEL responses or IDP redirects. The ZITADEL API is mocked, IDP redirects are simulated.
+- [ ] Playwright acceptances tests ensure that the happy paths of common user journeys work as expected. The ZITADEL API is not mocked but IDP redirects are simulated.
+- [ ] No debug or dead code
+- [ ] My code has no repetitions