refactor: update nightly build procedures (#32)

* install dependencies via flopy where possible
* prevent concurrent development builds, use `cancel-in-progress`
* remove `make_distribution.py`, call mf6 `release.yml` instead
* mention ubuntu 2022 libc compatibility issues in readme
* include code.json as a release asset

.github/workflows/full-dist-test.yml

@@ -0,0 +1,60 @@
+name: MODFLOW 6 full distribution test
+on:
+  schedule:
+    - cron: '0 2 * * *' # run at 2 AM UTC
+  push:
+    branches:
+      - master
+      - develop
+      - ci-diagnose*
+  pull_request:
+    branches:
+      - master
+jobs:
+  get_version:
+    name: Get current version
+    runs-on: ubuntu-22.04
+    defaults:
+      run:
+        shell: bash -l {0}
+    outputs:
+      version: ${{ steps.get_version.outputs.version }}
+    steps:
+
+      - name: Checkout repo
+        uses: actions/checkout@v3
+        with:
+          repository: MODFLOW-USGS/modflow6-nightly-build
+
+      - name: Checkout modflow6
+        uses: actions/checkout@v3
+        with:
+          repository: MODFLOW-USGS/modflow6
+          path: modflow6
+
+      - name: Setup Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: 3.9
+
+      - name: Install Python packages
+        run: pip install -r requirements.txt
+
+      - name: Get version
+        working-directory: modflow6/distribution
+        id: get_version
+        run: |
+          ver=$(python update_version.py -g)
+          echo "version=${ver}" >> "$GITHUB_OUTPUT"
+
+  make_dist:
+    name: Make full distribution
+    needs: get_version
+    uses: MODFLOW-USGS/modflow6/.github/workflows/release.yml@develop
+    with:
+      approve: false
+      branch: develop
+      developmode: false
+      full: true
+      run_tests: false
+      version: "${{ needs.get_version.outputs.version }}dev"