docs: improved SEO of documentation (#3117)

* docs: added description to documentation pages

* docs: added more descriptions

* docs: finished improving meta description

* docs: added searchbox structured data

* docs: added breadcrumbs structured data

* docs: added how to structured data

* docs: improved 404 page

* docs: added how-to frontmatter option

docs/content/user-guide/settings/currencies.md

@@ -1,5 +1,7 @@
 ---
 sidebar_position: 2
+description: 'This user guide explains how to manage currencies on the Medusa admin. Learn how to add currencies and set default currency.'
+addHowToData: true
 ---
 
 # Manage Currencies

docs/content/user-guide/settings/publishable-api-keys.mdx

@@ -1,5 +1,7 @@
 ---
 sidebar_position: 4
+description: 'This user guide explains how to manage publishable API keys on the Medusa admin. Learn how to create, edit, copy, and revoke publishable API keys.'
+addHowToData: true
 ---
 
 import UiIcon from '@site/src/components/UiIcon';

docs/content/user-guide/settings/return-reasons.mdx

@@ -1,5 +1,7 @@
 ---
 sidebar_position: 3
+description: 'This user guide explains how to manage return reasons on the Medusa admin. Learn how to add, edit, and remove return reasons.'
+addHowToData: true
 ---
 
 import UiIcon from '@site/src/components/UiIcon';

docs/content/user-guide/settings/store.md

@@ -1,5 +1,6 @@
 ---
 sidebar_position: 1
+description: 'This user guide explains how to manage the store details on the Medusa admin.'
 ---
 
 # Manage Store Details