chore(node): Upgrade to node lts

Upgrading the docker build and nvm to node 20.18, which is the latest
supported, stable LTS version. Node 12 and 16 have been EoL since April,
2022 and August, 2023, respectively. In addition, a transitive
dependency of mjml, minimatch, is not compatible with anything less than
node 14 at this point, so email generation from templates was broken.
With the move to newer node, I had to deal with a new node/docker
restriction which won't allow you to `npm install` in the root
directory. I wanted to maintain backwards compatiblity with current
installs and their MJML_PATH parameter, so I worked around the problem
by installing mjml in another directory and then moving node_modules to
the root directory. It's not pretty, but it worked. I'm trying to run
tests locally and I get one failure, but I'm not sure if it's my setup
or something I need to correct. I've manually tested the setup, gone
into every page, and not experienced problems.

Author: bashbreakpoint

.nvmrc

@@ -1 +1 @@
-16.13.0
+20.18.0

docker/Dockerfile

@@ -87,7 +87,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 RUN echo "deb http://apt.postgresql.org/pub/repos/apt bullseye-pgdg main" > /etc/apt/sources.list.d/pgdg.list \
     && wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
 
-RUN wget --quiet -O - https://deb.nodesource.com/setup_12.x | bash -
+RUN wget --quiet -O - https://deb.nodesource.com/setup_16.x | bash -
 
 COPY --from=sdist /dist/*.whl /tmp/dist/
 RUN buildDeps="" \
@@ -104,7 +104,21 @@ RUN buildDeps="" \
     pkg-config postgresql-client-14 nodejs \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/* \
-    && npm install mjml --no-cache-dir
+    # mjml has to be installed differently here because
+    # after node 14, docker will install npm files at the
+    # root directoy and fail, so we have to create a new
+    # directory and use it for the install then copy the
+    # files to the root directory to maintain backwards
+    # compatibility for email generation
+    && mkdir -p /mjml_install \
+    # if our workdir is /, then pushd/popd doesn't work
+    # for the npm install. It still tries to install in /,
+    # which npm can't do
+    && cd /mjml_install \
+    && npm install --no-cache-dir mjml \
+    && mv node_modules / \
+    && cd / \
+    && rm -rf /mjml_install
 
 EXPOSE 8000
 VOLUME /var/lib/dispatch/files