Lb/current user method

[elceebee]

Context

See slack thread: https://ukgovernmentdfe.slack.com/archives/C06962474AC/p1702994098513929

We need the current_user method to return a Service::User object, not a DfeSignInUser instance.

I did this as part of the support_user journey work, it makes sense to implement it earlier as needed in other places.

Changes proposed in this pull request

When a user is logged in a service, the current_user method returns the appropriate user object - Placements::User for the placements service, Claims::User for the claims service

No UI changes.

Guidance to review

Link to Trello card

Things to check

• [NA] If the code removes any existing feature flags, a data migration has also been added to delete the entry from the database
• [NA] This code does not rely on migrations in the same Pull Request
• [NA] If this code includes a migration adding or changing columns, it also backfills existing records for consistency
• [NA] If this code adds a column to the DB, decide whether it needs to be in analytics yml file or analytics blocklist
• [NA] API release notes have been updated if necessary
• [NA] If it adds a significant user-facing change, is it documented in the CHANGELOG?
• [NA] Required environment variables have been updated or added to the Azure KeyVault

Screenshots

[elceebee]

this is a quick fix for the persona test -- I'm actually splitting it into two different tests (one for claims, one for placements in the next PR, but I just want to get the current_user stuff in so we can all use it for now.

[elceebee]

Linting, not sure how this snuck in...

[JamieCleare2525]

Resolves the issue of User being assigned to :current_user