Create a container for all login

**Describe the task**
For all the login pages we can create a container and make a common pattern with slots. (Student has faqs which can be handled).

**Acceptance Criteria**
- [ ] Create a common container for login pages like full-page-container.
- [ ] Remove .sign-in-description class (no longer required)

**Additional context**
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Start by locating all login pages and the existing full-page-container pattern, then compare how the student FAQ content fits into a shared container with slots. Done means the login pages use the common container and the .sign-in-description class has been removed.

Written by the indexing model from the issue text.