fix(server): file persistence for local upload provider

[raymon-zhang]

Fix:

• create a data/rctf-uploads folder in the install script
• in the docker-compose file, create a docker bind mount from the data/rctf-uploads folder to /app/uploads in the rctf
• in the local upload provider, save and load uploadMap from the uploadMap.json file

[ginkoid]

if two rctf instances use the same uploads directory, we want them to be able to share uploads without a restart. can you do something similar to this? https://github.com/redpwn/rctf/blob/next/packages/server/src/providers/uploads/local/index.ts