[575] Change login page title when One Login is active

[elceebee]

Context

As an existing Apply user I might think 'I already have an account with Apply' so it is confusing (unless I read the smaller text on the page) why I'm being asked to create an account. Especially as the 'Apply for teacher training' service name is displayed.

Changes proposed in this pull request

• Change the title of the page
• Also moved the heading below the error summary (accessibility fix while I'm here)

With magic link	With One Login

Guidance to review

Link to Trello card

https://trello.com/c/02DkpuXs

Things to check

• If the code removes any existing feature flags, a data migration has also been added to delete the entry from the database
• This code does not rely on migrations in the same Pull Request
• If this code includes a migration adding or changing columns, it also backfills existing records for consistency
• If this code adds a column to the DB, decide whether it needs to be in analytics yml file or analytics blocklist, if included inform data insights team of the changes
• If this code adds a column that may include PII, the sanitise.sql script and 0025-protecting-personal-data-in-production-dump.md ADR have been updated.
• API release notes have been updated if necessary
• If it adds a significant user-facing change, is it documented in the CHANGELOG?
• Attach the PR to the Trello card

[elceebee]

Bug: One Login - Improve clarity of creation wording on "create or sign in" page