Confirm UK English spelling in Workday RaaS guide

[Copilot]

Addressed feedback on #325 to confirm UK English spelling convention for the Workday RaaS connector documentation.

Changes

• Verified "Optimised for Performance" uses UK English spelling (not "Optimized") at lines 56 and 106
• No code changes required - existing content already follows UK English conventions as requested

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Summary by cubic

Standardised the HRIS Workday RaaS Connector guide and ICC doc to UK English for consistency and clarity. Aligns with Linear INT-7705.

• Refactors
  • Converted spellings (organisation, authorised, centre, etc.).
  • Updated date formats (DD/MM/YYYY), punctuation, and examples to UK style.
  • Applied across both docs; no functional or content changes.

^{Written for commit 9cfce96. Summary will update automatically on new commits.}