github+make: check all CLI flags are in sample-lnd.conf

We add a GitHub action to our workflow that makes sure all command line
flags of lnd that are available with the default build tags are
contained in the sample-lnd.conf file.

.github/workflows/main.yml

@@ -202,6 +202,44 @@ jobs:
       - name: build mobile specific code
         run: go build --tags="mobile" ./mobile
 
+  ########################
+  # sample configuration check
+  ########################
+  sample-conf-check:
+    name: sample configuration check
+    runs-on: ubuntu-latest
+    steps:
+      - name: git checkout
+        uses: actions/checkout@v2
+
+      - name: go cache
+        uses: actions/cache@v1
+        with:
+          path: /home/runner/work/go
+          key: lnd-${{ runner.os }}-go-${{ env.GO_VERSION }}-${{ github.job }}-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            lnd-${{ runner.os }}-go-${{ env.GO_VERSION }}-${{ github.job }}-${{ hashFiles('**/go.sum') }}
+            lnd-${{ runner.os }}-go-${{ env.GO_VERSION }}-${{ github.job }}-
+            lnd-${{ runner.os }}-go-${{ env.GO_VERSION }}-
+            lnd-${{ runner.os }}-go-
+
+      - name: setup go ${{ env.GO_VERSION }}
+        uses: actions/setup-go@v2
+        with:
+          go-version: '~${{ env.GO_VERSION }}'
+
+      - name: download cache
+        uses: actions/cache@v1
+        with:
+          path: /home/runner/work/download_cache
+          key: lnd-${{ runner.os }}-download-${{ hashFiles('**/install_travis_proto.sh') }}
+          restore-keys: |
+            lnd-${{ runner.os }}-download-${{ hashFiles('**/install_travis_proto.sh') }}
+            lnd-${{ runner.os }}-download-
+
+      - name: check all command line flags exist in sample-lnd.conf file
+        run: make sample-conf-check
+
   ########################
   # run unit tests
   ########################