[StepSecurity] Apply security best practices (#4539)

Signed-off-by: StepSecurity Bot <bot@stepsecurity.io>

.github/dependabot.yml

@@ -0,0 +1,16 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily
+
+  - package-ecosystem: pip
+    directory: /docs/mkdocs
+    schedule:
+      interval: daily
+
+  - package-ecosystem: pip
+    directory: /tools/serve_header
+    schedule:
+      interval: daily