Add Github Action Super Linter (microsoft#7637)

This uses the templates from
https://github.com/github/super-linter/tree/master/TEMPLATES currently.
A future PR can add the necessary templates to the Windows Terminal
repository and update the source of Templates following the README.
Additionally we can add flags to explicitly choose the linters
applicable to this code base but is not necessary.

Per the README, this does not enforce any linting rules but rather
outputs the suggestions in the build step, which are to be read by the
PR submitter and Windows Terminal team to determine if they want to use
the linting rule. C++ is currently not supported (Powershell, Json,
Yaml, and Markdown will be the only things the linter checks for
currently) but we could add our own custom support if desired in
separate PR.

## Validation Steps Performed
It successfully runs. Currently only shows the yaml file itself being
linted in this PR as a test case. It will apply to new PRs once this is
merged. We can lint existing code base but would require a separate PR
and examining the code output (also requires updating the yaml file
temporarily).

Closes microsoft#7513

.github/workflows/linter.yml

@@ -0,0 +1,49 @@
+---
+###########################
+###########################
+## Linter GitHub Actions ##
+###########################
+###########################
+name: Lint Code Base
+
+#
+# Documentation:
+# https://help.github.com/en/articles/workflow-syntax-for-github-actions
+#
+
+#############################
+# Start the job on all push #
+#############################
+on:
+  pull_request:
+    branches: [master]
+
+###############
+# Set the Job #
+###############
+jobs:
+  build:
+    # Name the Job
+    name: Lint Code Base
+    # Set the agent to run on
+    runs-on: ubuntu-latest
+
+    ##################
+    # Load all steps #
+    ##################
+    steps:
+      ##########################
+      # Checkout the code base #
+      ##########################
+      - name: Checkout Code
+        uses: actions/checkout@v2
+
+      ################################
+      # Run Linter against code base #
+      ################################
+      - name: Lint Code Base
+        uses: github/super-linter@v3.10.0
+        env:
+          VALIDATE_ALL_CODEBASE: false
+          DEFAULT_BRANCH: master
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}