chore: moving ordering to category jsons and frontmatters (#3777)

# Description

This big PR does a simple thing: It makes pages ordering respect
metadata instead of filenames

## Problem\*

A naive approach supported over the years at docusaurus was to simply
have files prefixed with 00, 01, 02, which were removed automatically by
docusaurus.

This makes docs a bit harder to maintain if for some reason you decide
to move pages around, as it breaks all the links.

## Summary\*

- Renames all the folders and pages to remove the prefixes
- Adds `sidebar_position` property in frontmatter, to order them 
- Adds `_category_.json` files to order folders
- Removes ordering of top level folders in `sidebars.json`

Author: signorecello

docs/docs/explanations/_category_.json

@@ -0,0 +1,5 @@
+{
+    "position": 3,
+    "collapsible": true,
+    "collapsed": true
+}

docs/docs/explanations/modules_packages_crates/_category_.json

@@ -0,0 +1,6 @@
+{
+    "label": "Modules, Packages and Crates",
+    "position": 2,
+    "collapsible": true,
+    "collapsed": true
+}

…s_packages_crates/crates_and_packages.md …s_packages_crates/crates_and_packages.mddocs/docs/explanations/02_modules_packages_crates/crates_and_packages.md renamed to docs/docs/explanations/modules_packages_crates/crates_and_packages.md docs/docs/explanations/02_modules_packages_crates/crates_and_packages.md renamed to docs/docs/explanations/modules_packages_crates/crates_and_packages.md

@@ -0,0 +1,6 @@
+{
+    "label": "Noir",
+    "position": 0,
+    "collapsible": true,
+    "collapsed": true
+}