feat: Add Pashto (ps) locale

[snehal242005]

Closes #171 (partially - adds one more requested locale)

What does this PR do?

Adds the Pashto (ps) locale to Day.js, following the same structure
as fa.js, ur.js, and af.js.

Pashto is spoken by 40-60 million people and is one of the two
official languages of Afghanistan (alongside Dari/Persian), but was
not yet supported.

Data sources

Day/month names, week start (Saturday, matching Afghanistan
convention), and relative time patterns were sourced directly from
the Unicode CLDR dataset (cldr-json/cldr-dates-full/main/ps/)
rather than transliterated from memory, to ensure accuracy.

Notes for reviewers

• weekdaysMin was intentionally omitted, following the same pattern
  as fa/ur - Day.js falls back to the first 2 characters of the
  full weekday name when absent, which works correctly here.
• ordinal returns the number as-is (no suffix), matching the
  precedent set by fa.js/ur.js for Perso-Arabic script locales.
• CLDR's weekday forms are numeral-based coinages. If maintainers or
  native speakers prefer the more commonly-used Persian-loanword
  forms instead, happy to update based on feedback.

Checklist

• Follows existing locale file structure/conventions
• Sourced from authoritative CLDR data
• No existing tests broken (Day.js has no central locale registry
  requiring updates)