Update REST API Handbook: Replace _filter with _fields in Pages Schema Section

[dhruvang21]

Created issue on contribution day at Wordcamp Ahmedabad.

Issue Description

In the REST API handbook page for "Pages," under the Schema section, the _filter parameter is incorrectly documented. This parameter has been removed from the WordPress REST API and replaced with _fields.

URL of the Page with the Issue

https://developer.wordpress.org/rest-api/reference/pages/

Section of Page with the issue

The "Schema" section where _filter is mentioned.

Why is this a problem?

The documentation contains outdated information about the _filter parameter, which may mislead developers into using a parameter that no longer exists. The correct parameter, _fields, needs to be documented to ensure accurate and up-to-date guidance.

Suggested Fix

Replace all instances of _filter in the Schema section with _fields, reflecting the current REST API implementation. Additionally, ensure that any examples or descriptions associated with _filter are updated to _fields.

[github-actions]

Heads up @WordPress/docs-issues-coordinators, we have a new issue open. Time to use 'em labels.