feat: add documented component to uffizzi environment

So far, none of the components at the uffizzi environment have techdocs.
Hence, there are no docs available within this environment
and related features are not covered.

This change will add an example from techdocs-backend plugin
to the deployed examples.

It was possible to register this catalog file manually,
however the build of the docs fail due to missing Docker.

To allow the generation of docs, we use the local generator
(no docker in docker) and install required dependencies.

As we don't want all dependencies for all (default) extensions
to be installed at this environment, the original example at
techdocs-backend plugin was copied and reduced
(PlantUML extension example was removed).

Signed-off-by: Patrick Jungermann <Patrick.Jungermann@gmail.com>

packages/backend/Dockerfile

@@ -13,11 +13,14 @@ FROM node:16-bullseye-slim
 
 # Install sqlite3 dependencies. You can skip this if you don't use sqlite3 in the image,
 # in which case you should also move better-sqlite3 to "devDependencies" in package.json.
+# Additionally, we install dependencies for `techdocs.generator.runIn: local`.
+# https://backstage.io/docs/features/techdocs/getting-started#disabling-docker-in-docker-situation-optional
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt,sharing=locked \
     apt-get update && \
-    apt-get install -y --no-install-recommends libsqlite3-dev python3 build-essential && \
-    yarn config set python /usr/bin/python3
+    apt-get install -y --no-install-recommends libsqlite3-dev python3 python3-pip build-essential && \
+    yarn config set python /usr/bin/python3 && \
+    pip3 install mkdocs-techdocs-core==1.1.7
 
 # From here on we use the least-privileged `node` user to run the backend.
 WORKDIR /app