Add a devcontainer, since the default for codespaces is node 16 :0

Author: brendandburns

.devcontainer/devcontainer.json

@@ -0,0 +1,4 @@
+{
+    "name": "Node.js",
+    "image": "mcr.microsoft.com/devcontainers/javascript-node:1-22-bookworm"
+}

.github/dependabot.yml

@@ -5,6 +5,7 @@ updates:
       schedule:
           interval: 'daily'
           time: '02:00'
+      target-branch: 'main'
     - package-ecosystem: 'npm'
       directory: '/'
       target-branch: 'master'
@@ -16,3 +17,9 @@ updates:
       schedule:
           interval: 'daily'
           time: '03:00'
+      target-branch: 'main'
+    - package-ecosystem: 'devcontainers'
+      directory: '/'
+      schedule:
+          interval: 'weekly'
+      target-branch: 'main'