Enter an ECT's national insurance number to match a TRS record

[TobyRet]

Ticket

512

Changes

• Add a 'national insurance number' step to the Register ECT flow and direct the user to this step if TRS API cannot find a teacher with the submitted date of birth and TRN
• Wire up national insurance number validator
• Direct the user to a 'not found' page if the TRS API can still not find a teacher with the submitted national insurance number
• Add national insurance numbers to test guidance component
• Refactoring: create a factory to handle storage for each step in the flow

Vids

Enter national insurance number

https://github.com/user-attachments/assets/9b407cfd-21f7-4645-b1a1-131e9ad57ba5

Teacher not found

https://github.com/user-attachments/assets/c11881d2-6107-410b-aab2-1154367d7f46