### What
To reduce the work needed, this PR adds paths-ignore to avoid building
unnecessary workflows.
Co-authored-by: Gastón Fournier <gaston@getunleash.io>
## About the changes
Reduce the build time of OSS docker image from
[~30m](https://github.com/Unleash/unleash/actions/workflows/docker_publish.yaml)
to [under
15m](https://github.com/Unleash/unleash/actions/runs/5222180536/jobs/9427342758)
1. Build frontend outside docker multiplatform.
2. Allow `frontend/build` to be copied to the image by removing this
from `.dockerignore`
3. Run with `--ignore-scripts` to avoid building the frontend on the
`prepare` script, but this requires us to run all the prepare scripts
manually (except the frontend build).
**Note:** we need to build frontend in the `prepare` script to be able
to have source code dependencies
## Manual Testing
Manually downloaded from
https://hub.docker.com/r/unleashorg/unleash-server/tags?page=1 and
compared both `unleash` folders from main and the version built with the
new process
https://github.com/Unleash/unleash/actions/runs/5223078089/jobs/9429430190#step:5:48
No major difference was spotted (only expected changes due to
development done in main)
**Command used to extract the contents:**
```
cd /tmp
mkdir main && cd main
docker pull unleashorg/unleash-server:main-edge-18-alpine
docker export $(docker create unleashorg/unleash-server:main-edge-18-alpine) > container.tar && tar xvf container.tar
mkdir ../new-process && cd ../new-process
docker pull unleashorg/unleash-server:sha-ccac902-18-alpine
docker export $(docker create unleashorg/unleash-server:sha-ccac902-18-alpine) > container.tar && tar xvf container.tar
meld ./unleash ../main/unleash
```
