feat: ofsted data points optional for gias submission

[J05h-L]

Context

AB#241881 - AB#246016

Change proposed in this pull request

New gias input schema created. Following the existing pattern for input schemas default for the existing schema for historic processing and a new 2024 with the following columns omitted.

• OfstedRating (name)
• OfstedLastInsp

Changes to prepare_schools_data in pre_processing\ancillary\schools.py to accommodate the above.

The omitted columns are required to write to the db and OfstedRating (name) is a factor for rag calculations.

Therefore if not present in the submission these columns are created with default values.

• OfstedRating (name) as an empty string. Later in rag.py this will resolve to "other" and not be considered for rag rating calculations. ie != "outstanding"
• OfstedLastInsp as None (NaT for pd.to_datetime, NULL for the db)
  This aligns with current behaviour when these values are missing for a row.

If present in the submission the current behaviour is preserved.

Tests added to confirm the above.

Guidance to review

When running locally no changes to 2021 - 2023 default runs should be observed.

For 2024 all_schools.parquet OfstedRating (name) and OfstedLastInsp should only contain the default values.

Also for a 2024 run the latest gias all establishment data > establishment fields can be processed without error.

Checklist (add/remove as appropriate)

• Work items have been linked (use AB#)
• Your code builds clean without any errors or warnings
• You have run all unit/integration tests and they pass
• Your branch has been rebased onto main
• You have tested by running locally

[jrabbott]

LGTM - would appreciate @PsypherPunk eyes on the mappings

[PsypherPunk]

Functionally, with one stray print(), this LGTM; a couple of minor quibbles.