[Builder] Change registry URL configurations

[Hedingber]

• Move builder configuration to use the main config.py instead of reading from env var directly, this caused a change with the env vars naming: DEFAULT_DOCKER_REGISTRY -> MLRUN_HTTPDB__BUILDER__DOCKER_REGISTRY, DEFAULT_DOCKER_SECRET -> MLRUN_HTTPDB__BUILDER__DOCKER_REGISTRY_SECRET
• Added support to giving the docker repository inside the registry config value, which will override the default repository (mlrun)
• Added logic in config so that when dbpath is being set we connect to the db (API) which will sync config from it
• Bump kaniko tag - I had a bug similar Long builds fail with "UNAUTHORIZED: \"authentication required\"" GoogleContainerTools/kaniko#245 and upgrade solved it
• related docs fixes
• Reordered the jupyter dockerfile to improve caching