[CI] Moves lint and docs tasks to Buildkite

.buildkite/pipeline.yml

@@ -1,4 +1,16 @@
 steps:
+  - label: ":python: Lint code and build documentation"
+    agents:
+      provider: "gcp"
+    commands:
+      - "echo --- :python: Installing dependencies"
+      - "sudo apt-get update"
+      - "sudo apt-get install --yes pandoc python3 python3-pip"
+      - "python3 -m pip install nox"
+      - "echo --- :terminal: Linting the code"
+      - "nox -s lint"
+      - "echo --- :books: Building documentation"
+      - "nox -s docs"
   - label: "Eland :python: {{ matrix.python }} :elasticsearch: {{ matrix.stack }}"
     agents:
       provider: "gcp"