O3-5334: Add WHO growth standards JSON data

[dilankavishka]

Requirements

• This PR has a title that briefly describes the work done including the ticket number. If there is a ticket, make sure your PR title includes a conventional commit label. See existing PR titles for inspiration.
• My work is based on designs, which are linked or shown either in the Jira ticket or the description below. (See also: Styleguide)
• My work includes tests or is validated by existing tests.

Summary

This PR integrates the official WHO Child Growth Standards (Weight-for-Age, 0-5 years) into the application. The original WHO CSV datasets have been converted into optimized JSON files to support both Z-score calculations (using L, M, S parameters) and chart visualization (using percentile values). Additionally, the README.md has been updated to document the data schema and sources.

Link to WHO data - Here

Related Issue

https://openmrs.atlassian.net/browse/O3-5334

Other

[dilankavishka]

@anjula-sack @denniskigen @NethmiRodrigo Could you please review this?