[SG-656] Send a captcha bypass token back from the register endpoint

[addisonbeck]

https://bitwarden.atlassian.net/jira/software/c/projects/SG/boards/71?modal=detail&selectedIssue=SG-656

This will be part of a cloud server hotfix.

Type of change

- [x] Bug fix
- [ ] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

The trial initiation flow has a registration step that automatically does a login in the background. This has Captcha problems, namely that it can spawn two captchas in a row - one during registration and one during login. This is not ideal UX, so we've added a bypass token that returns from the registration endpoint that can be used to skip the next captcha.

bitwarden/clients#3531 depends on this change.

Code changes

• Create a model to encapsulate a RegistrationResponse
• Generate a user CaptchaBypassToken after a successful registration that we return to caller.

Before you submit

• Please check for formatting errors (dotnet format --verify-no-changes) (required)
• If making database changes - make sure you also update Entity Framework queries and/or migrations
• Please add unit tests where it makes sense to do so (encouraged but not required)
• If this change requires a documentation update - notify the documentation team
• If this change has particular deployment requirements - notify the DevOps team

[differsthecat]

Nice solution!