Add concept mapping for baseline fields (e.g. BMI measurement)

[MaximMoinat]

We have not included BMI (field 21001) in the baseline field mappings. Therefore it is ignored. We should add this AND not ignore baseline fields for which a mapping is missing.

Same for 22420 - LV ejection fraction #325.

• Review unprioritised fields for other important fields to include (1)
• Look into using the new OMOP UKB vocabulary, to reuse the 'Maps to' (1)
• Add mapping for the identified important fields (2)
• Test (1)

[MaximMoinat]

An overview from UCL of missing mappings available here: https://docs.google.com/spreadsheets/d/1VAoA4DVb19eYY4kik8Nw5eJzo_Dn8m9fgCVcMNXARPE/edit#gid=1677770576

Marked in blue are missing UKB fields with priority. We should at least make sure a mapping for these is included.

[MaximMoinat]

Made a start in linked PR.
To do:

• Go through the new discrete_fields.csv mapping in Usagi, specifically the Recent medication, tobacco/smoking status, alcohol consumpiton and mental health fields
• Create mappings for all numeric fields from UKB vocabulary (prioritised and not prioritised). With both maps to and maps to unit.