add short titles to frontmatter (#20131)

content/github/extending-github/getting-started-with-the-api.md

@@ -6,6 +6,7 @@ versions:
   fpt: '*'
   ghes: '*'
   ghae: '*'
+shortTitle: Get started API
 ---
 
 To automate common tasks, back up your data, or create integrations that extend {% data variables.product.product_name %}, you can use the {% data variables.product.product_name %} API.

content/github/extending-github/git-automation-with-oauth-tokens.md

@@ -9,6 +9,7 @@ versions:
   fpt: '*'
   ghes: '*'
   ghae: '*'
+shortTitle: Automate with OAuth tokens
 ---
 
 ## Step 1: Get an OAuth token