Auto-label PRs based on their content (#7044)

This PR adds the GitHub action [PR Labeler](https://github.com/actions/labeler) to auto-label PRs based on their content. 

Labeling is managed with a configuration file `.github/labeler.yml` using the following [options](https://github.com/actions/labeler#usage).

Authors:
  - Joseph (@jolorunyomi)
  - Mike Wendt (@mike-wendt)

Approvers:
  - AJ Schmidt (@ajschmidt8)
  - Keith Kraus (@kkraus14)
  - Mike Wendt (@mike-wendt)

URL: #7044

.github/labeler.yml

@@ -0,0 +1,21 @@
+# Documentation for config - https://github.com/actions/labeler#common-examples
+
+cuDF (Python):
+  - 'python/**'
+  - 'notebooks/**'
+
+libcudf:
+  - 'cpp/**'
+
+CMake:
+  - '**/CMakeLists.txt'
+  - '**/cmake/**'
+
+cuDF (Java):
+  - 'java/**'
+
+gpuCI:
+  - 'ci/**'
+
+conda:
+  - 'conda/**'

.github/workflows/labeler.yml

@@ -0,0 +1,11 @@
+name: "Pull Request Labeler"
+on:
+- pull_request_target
+
+jobs:
+  triage:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@main
+      with:
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"