Sentence-case param names

[anth-volk]

The params are inconsistent, with some in title case, some in sentence case, and some being acronyms, making it hard to apply one visual style correctly

[anth-volk]

@PolicyEngine Open a PR applying sentence case to the "label" fields of the parameter metadata in this package. Make sure not to de-capitalize proper names or acronyms, like "Bank of England" or "HMRC".

[policyengine]

✅ Complete! Standardized all parameter labels to sentence case.

Converted 141 parameter files while preserving proper names (Bank of England, Child Benefit, etc.) and acronyms (HMRC, VAT, NHS, etc.).

Examples:

• private school VAT rate → Private school VAT rate
• tax on consumers (£bn) → Tax on consumers (£bn)
• Personal Allowance phase-out rate → Personal allowance phase-out rate

Pull request: #1462