Add Dependabot approve action workflow

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

.github/dependabot-approve.workflow

+workflow "Approve Dependabot PRs" {
+  resolves = ["hmarr/auto-approve-action@v1.0.0"]
+  on = "push"
+}
+
+action "Filters for GitHub Actions" {
+  uses = "actions/bin/filter@3c0b4f0e63ea54ea5df2914b4fabf383368cd0da"
+  args = "actor dependabot-preview"
+}
+
+action "hmarr/auto-approve-action@v1.0.0" {
+  uses = "hmarr/auto-approve-action@v1.0.0"
+  needs = ["Filters for GitHub Actions"]
+  secrets = ["GITHUB_TOKEN"]
+}