[api-docs] follow the correct schema for frontmatter (#138348)

* [api-docs] follow the correct schema for frontmatter

* rename non-generated summary: usage

* fix yaml comment syntax

dev_docs/getting_started/dev_welcome.mdx

@@ -2,7 +2,7 @@
 id: kibDevDocsWelcome
 slug: /kibana-dev-docs/getting-started/welcome
 title: Welcome
-summary: Build custom solutions and applications on top of Kibana.
+description: Build custom solutions and applications on top of Kibana.
 date: 2021-01-02
 tags: ['kibana', 'dev', 'contributor']
 ---

dev_docs/getting_started/hello_world_plugin.mdx

@@ -2,7 +2,7 @@
 id: kibHelloWorldApp
 slug: /kibana-dev-docs/getting-started/hello-world-app
 title: Hello World
-summary: Build a very basic plugin that registers an application that says "Hello World!".
+description: Build a very basic plugin that registers an application that says "Hello World!".
 date: 2021-08-03
 tags: ['kibana', 'dev', 'contributor', 'tutorials']
 ---

dev_docs/getting_started/setting_up_a_development_env.mdx

@@ -2,7 +2,7 @@
 id: kibDevTutorialSetupDevEnv
 slug: /kibana-dev-docs/getting-started/setup-dev-env
 title: Set up a Development Environment
-summary: Learn how to setup a development environment for contributing to the Kibana repository
+description: Learn how to setup a development environment for contributing to the Kibana repository
 date: 2022-07-07
 tags: ['kibana', 'onboarding', 'dev', 'architecture', 'setup']
 ---

dev_docs/getting_started/troubleshooting.mdx

@@ -2,7 +2,7 @@
 id: kibTroubleshooting
 slug: /kibana-dev-docs/getting-started/troubleshooting
 title: Troubleshooting
-summary: A collection of tips for working around strange issues.
+description: A collection of tips for working around strange issues.
 date: 2021-09-08
 tags: ['kibana', 'onboarding', 'dev', 'troubleshooting']
 ---