energy_price_cap_levels_annex_9: Remove VAT from electricity bills for Oct 2026 and Jan 2026 price caps

[eglucas]

As per gov announcement made on 21 July: https://www.gov.uk/government/news/new-pm-cuts-tax-on-household-electricity-bills-to-give-breathing-space-on-cost-of-living

Government is tackling rising bills with a tax cut to remove VAT from domestic electricity bills from October 1 in time to impact the next Ofgem price cap. This immediate action applies and is funded for this financial year.

This must be done when the new price cap is released and new Annex 9 is published on 26 August

[eglucas]

This will be fixed alongside issue #79 (updating medium TDCVs that scale the 1c consumption adjusted levels table).

The next price cap is expected to be published Weds Aug 26th. We can't know with full certainty exactly how Ofgem will change the spreadsheet to reflect (i) new TDCVs, and (ii) VAT coming off electricity for the Oct - Dec 2026 and Jan - Mar 2027 price caps.

Plan of action to prepare for this next price cap release, how pipeline will be run and dashboard updated on the day:

• [prep] Make pipeline code changes in feature branch
• [prep] Need to have a script or notebook ready to run so checks on this morning will be fast
• [on the day] On Aug 26, when new Annex 9 file has been published on the Ofgem website, run the pipeline from feat branch -> make sure it runs successfully -> updated data lands in dev bucket
• [on the day] Inspect the data by reading the parquet file from dev bucket and run the prepared checks
• [on the day] Once verified, merge to dev
• [on the day] Promote dev to prod
• [on the day] Run pipeline on prod
• [on the day] Wait for DuckLake to pick up latest data in prod bucket
• [on the day] Verify new data has landed in Superset