Convert original extract to factors for health board/simd/etc

[aoifem01]

Converting health board and SIMD to factors instead of characters should mean we don't need to do left_join to hb_tibble etc, can just use complete() instead - makes things slightly tidier and can keep levels consistent throughout analysis

[aoifem01]

instead of this, make a function that does it for us i.e. takes a df and left joins it to the things you want it joined by (hbres, simd, etc)