Add basic devcontainer.json based on ftl-build for x86_64 arch, with a few helpful extensions.

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

.devcontainer/devcontainer.json

@@ -0,0 +1,10 @@
+{
+  "name": "FTL x86_64 Build Env",  
+  "image": "ghcr.io/pi-hole/ftl-build:x86_64", 
+  "extensions": [
+    "jetmartin.bats",
+    "ms-vscode.cpptools",
+    "ms-vscode.cmake-tools",
+    "eamodio.gitlens"
+  ],  
+}

.gitignore

@@ -22,3 +22,7 @@ tools/macvendor.db
 
 # Test dependencies
 /node_modules/
+
+# Test Leftovers
+dig.log
+ptr.log