create flist server

[rawdaGastan]

Create a server to expose docker images conversion API

Related issue: https://github.com/threefoldtech/home/issues/1497

[rawdaGastan]

Tasks

• [x] add endpoint to create flist and return job ID for it to be tracked
• [x] add endpoint to get the status of the flist using the job ID
• [x] add endpoint to check the health of the server
• [x] add endpoint to signin (authentication)
• [x] add endpoint to list flists of the user. (templates are added)
• [x] add endpoint to get the list of flists per username
• [x] add authorization middleware to endpoints except health check
• [x] support authentication using list of users (username and password per user)
• [x] add server configurations (host, port, store_url, flist_dir, jwt_secret, jwt_expire, users)
• [x] add cors for endpoints
• [x] swagger
• [x] add validations for request bodies
• [x] add validations for configurations

[rawdaGastan]

• [ ] clean map of job and status for flists // to be discussed
• [ ] add pagination for listing flists
• [x] support progress for conversion (https://github.com/threefoldtech/rfs/issues/69)
• [x] preview flist (https://github.com/threefoldtech/rfs/pull/72)