[docs] Migrate docs from AsciiDoc to Markdown (#2635)

* delete asciidoc files

* add migrated files

* Apply suggestions from review

Co-authored-by: Josh Mock <josh@joshmock.com>

* Apply suggestions from review

Co-authored-by: Josh Mock <josh@joshmock.com>

* add the new ci checks (#2634)

---------

Co-authored-by: Marci W <333176+marciw@users.noreply.github.com>
Co-authored-by: Josh Mock <josh@joshmock.com>

docs/reference/exists_examples.md

@@ -0,0 +1,44 @@
+---
+mapped_pages:
+  - https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/exists_examples.html
+---
+
+# Exists [exists_examples]
+
+Check that the document `/game-of-thrones/1` exists.
+
+::::{note}
+Since this API uses the `HEAD` method, the body value will be boolean.
+::::
+
+
+```js
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({
+  cloud: { id: '<cloud-id>' },
+  auth: { apiKey: 'base64EncodedKey' }
+})
+
+async function run () {
+  await client.index({
+    index: 'game-of-thrones',
+    id: '1',
+    document: {
+      character: 'Ned Stark',
+      quote: 'Winter is coming.'
+    }
+  })
+
+  const exists = await client.exists({
+    index: 'game-of-thrones',
+    id: 1
+  })
+
+  console.log(exists) // true
+}
+
+run().catch(console.log)
+```
+