feat(pipeline): ingest GIAS OfficialSixthForm into staging

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pipeline/plugins/extractors/tap-uk-gias/tap_uk_gias/tap.py

@@ -33,6 +33,7 @@ class GIASEstablishmentsStream(Stream):
         th.Property("EstablishmentName", th.StringType),
         th.Property("TypeOfEstablishment (name)", th.StringType),
         th.Property("PhaseOfEducation (name)", th.StringType),
+        th.Property("OfficialSixthForm (name)", th.StringType),
         th.Property("LA (code)", th.StringType),
         th.Property("LA (name)", th.StringType),
         th.Property("EstablishmentNumber", th.StringType),

pipeline/transform/models/staging/stg_gias_establishments.sql

@@ -14,6 +14,7 @@ renamed as (
         "EstablishmentName"                             as school_name,
         "TypeOfEstablishment (name)"                    as school_type,
         "PhaseOfEducation (name)"                       as phase,
+        nullif(trim("OfficialSixthForm (name)"), '')    as official_sixth_form,
         "Gender (name)"                                 as gender,
         "ReligiousCharacter (name)"                     as religious_character,
         "AdmissionsPolicy (name)"                       as admissions_policy,