Add GitHub Actions workflows

These are copied from https://github.com/lsst/testdata_ci_hsc/tree/main

.github/workflows/lint.yaml

@@ -0,0 +1,11 @@
+name: lint
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  call-workflow:
+    uses: lsst/rubin_workflows/.github/workflows/lint.yaml@main

.github/workflows/rebase_checker.yaml

@@ -0,0 +1,8 @@
+---
+name: Check that 'main' is not merged into the development branch
+
+on: pull_request
+
+jobs:
+  call-workflow:
+    uses: lsst/rubin_workflows/.github/workflows/rebase_checker.yaml@main

.github/workflows/shellcheck.yaml

@@ -0,0 +1,15 @@
+name: shellcheck
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Run shellcheck
+        uses: ludeeus/action-shellcheck@master
+        # See https://github.com/ludeeus/action-shellcheck for customizations