[FEAT] argilla server: Parameterize uvicorn app for extended apps (#5452)

# Description
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Please also include relevant motivation and context. List any
dependencies that are required for this change. -->

This PR adds a minimal change to allow users to extend in an easy (but
not easiest) server app. Users can use an extended version of the
FastAPI app including their endpoints when launching the docker
container by setting the `UVICORN_APP` environment variable.

This is related to this [discord
thread](https://discord.com/channels/879548962464493619/1278288595312054363)

An example of usage
[here](https://huggingface.co/spaces/frascuchon/extend-argilla-api-example/tree/main)

**Type of change**
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PR according to the type of change -->

- Improvement (change adding some improvement to an existing
functionality)

**How Has This Been Tested**
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**Checklist**
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- I added relevant documentation
- I followed the style guidelines of this project
- I did a self-review of my code
- I made corresponding changes to the documentation
- I confirm My changes generate no new warnings
- I have added tests that prove my fix is effective or that my feature
works
- I have added relevant notes to the CHANGELOG.md file (See
https://keepachangelog.com/)

Author: frascuchon

argilla-server/docker/server/Dockerfile

@@ -24,6 +24,8 @@ ENV API_KEY=""
 ENV ARGILLA_HOME_PATH=/var/lib/argilla
 ## Uvicorn defaults
 ENV UVICORN_PORT=6900
+### Uvicorn app. Extended apps can override this variable
+ENV UVICORN_APP=argilla_server:app
 
 RUN useradd -ms /bin/bash argilla
 
@@ -40,6 +42,7 @@ VOLUME $ARGILLA_HOME_PATH
 COPY scripts/start_argilla_server.sh /home/argilla
 # Destination folder must be the same as the builder one. Otherwise installed script won't work (since the installation fixes the path inside the script)
 COPY --chown=argilla:argilla --from=builder /opt/venv /opt/venv
+
 ENV PATH="/opt/venv/bin:$PATH"
 
 WORKDIR /home/argilla

argilla-server/docker/server/scripts/start_argilla_server.sh

@@ -37,4 +37,5 @@ fi
 #   with the prefix UVICORN_. For example, in case you want to
 #   run the app on port 5000, just set the environment variable
 #   UVICORN_PORT to 5000.
-python -m uvicorn argilla_server:app --host "0.0.0.0"
+
+python -m uvicorn $UVICORN_APP --host "0.0.0.0"

argilla/docs/reference/argilla-server/configuration.md

@@ -100,6 +100,7 @@ The following environment variables are useful only when PostgreSQL is used:
 
 - `API_KEY`: The default user api key to user. If API_KEY is not provided, a new random api key will be generated (Default: `""`).
 
+- `UVICORN_APP`: [Advanced] The name of the FastAPI app to run. This is useful when you want to extend the FastAPI app with additional routes or middleware. The default value is `argilla_server:app`.
 
 ## REST API docs