Cleanup onCreateNode in the gatsby-node file (codesandbox#2420)

* Cleanup gatsby-node

* Create generic node fields for all Markdown files

* Use editLink in Docs

* Add support for creating specific node fields for Markdown files

* Add Jobs specific node fields

* Use new Jobs node fields

* Add + use Docs specific node fields

* Add Blog specific node fields

* Use new Blog node fields

* Introduce createNodeFieldsFromNodeInfo to simplify some things

* Add Legal specific node fields

Author: MichaelDeBoey

packages/homepage/content/articles/announcing-codesandbox-2-0/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: announcing-codesandbox-2-0
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/announcing-codesandbox-2-5/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: announcing-codesandbox-2-5
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/announcing-codesandbox-containers/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: announcing-codesandbox-containers
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/announcing-codesandbox-custom-templates/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: Templates
 authors: ['Drake Costa']
 photo: https://avatars0.githubusercontent.com/u/3144549?s=460&v=4

packages/homepage/content/articles/announcing-codesandbox-dashboard-teams/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: announcing-codesandbox-dashboard-teams
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/announcing-codesandbox-v3/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: announcing-codesandbox-v3
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/codesadbox-introducing-improved-crash-reporting/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: CodeSadbox
 authors: ['Drake Costa']
 photo: https://avatars0.githubusercontent.com/u/3144549?s=460&v=4

packages/homepage/content/articles/codesandbox-1-5-changelog/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: codesandbox-1-5-changelog
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/codesandbox-an-online-react-editor/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: codesandbox-an-online-react-editor
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4

packages/homepage/content/articles/codesandbox-containers-out-of-beta-improvements/index.md

@@ -1,5 +1,5 @@
 ---
-featuredImage: ./images/banner.png
+banner: ./images/banner.png
 slug: codesandbox-containers-out-of-beta-improvements
 authors: ['Ives van Hoorne']
 photo: https://avatars0.githubusercontent.com/u/587016?s=460&v=4