docs(samples): add samples lint job and fix lint issues (#684)

* changes without context

        autosynth cannot find the source of changes triggered by earlier changes in this
        repository, or by version upgrades to tools such as linters.

* chore(java_templates): add lint/static analysis presubmit checks for samples

* chore(java_templates): add lint/static analysis presubmit checks for samples

* chore: fix trailing whitespace

Source-Author: Jeff Ching <chingor@google.com>
Source-Date: Mon Aug 17 14:29:16 2020 -0700
Source-Repo: googleapis/synthtool
Source-Sha: c3caf0704f25a0c365f1c315e804a30b87c62a75
Source-Link: googleapis/synthtool@c3caf07

* chore(java_templates): stop running pmd/spotbugs checks for samples

This was creating too much noise. We will revisit with other options and/or tune these checks.

Source-Author: Jeff Ching <chingor@google.com>
Source-Date: Wed Aug 19 12:26:49 2020 -0700
Source-Repo: googleapis/synthtool
Source-Sha: 9602086c6c5b05db77950c7f7495a2a3868f3537
Source-Link: googleapis/synthtool@9602086

.github/workflows/samples.yaml

@@ -0,0 +1,14 @@
+on:
+  pull_request:
+name: samples
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: 8
+      - name: Run checkstyle
+        run: mvn -P lint --quiet --batch-mode checkstyle:check
+        working-directory: samples/snippets