Enable backup restore

[LongLiveCHIEF]

• creates /octoprint/octoprint and /octoprint/plugins folders explicitly during docker build
• starts octoprint service using --basedir /octoprint/octoprint instead of just /octoprint
• changes the recommended mount path for the config-editor container to octoprint:/octoprint
  • updates the example and test compose files and README instructions to reflect this change

BREAKING CHANGES This may be a breaking change for existing users that are using a volume mounting strategy other than the recommended strategy, thus will constitue a new major release for the image.

Where before the root context of the volume mount looked like this:

/octoprint
├── config.backup
├── config.yaml
├── data
│   ├── announcements
│   ├── appkeys
│   ├── backup
│   ├── pluginmanager
│   ├── preemptive_cache_config.yaml
│   └── softwareupdate
├── generated
│   └── webassets
├── logs
│   ├── octoprint.log
│   ├── plugin_bedlevelvisualizer_debug.log
│   ├── plugin_pluginmanager_console.log
│   └── plugin_softwareupdate_console.log
├── octoprint
│   ├── config.backup
│   ├── config.yaml
│   ├── data
│   ├── generated
│   ├── logs
│   ├── plugins
│   ├── printerProfiles
│   ├── scripts
│   ├── slicingProfiles
│   ├── timelapse
│   ├── translations
│   ├── uploads
│   ├── users.yaml
│   ├── virtualSd
│   └── watched
├── plugins
│   ├── bin
│   └── lib
├── printerProfiles
│   └── _default.profile
├── scripts
├── slicingProfiles
├── timelapse
│   └── tmp
├── translations
├── uploads
├── virtualSd
└── watched

It will now look like this:

/octoprint
├── octoprint
│   ├── config.backup
│   ├── config.yaml
│   ├── data
│   ├── generated
│   ├── logs
│   ├── plugins
│   ├── printerProfiles
│   ├── scripts
│   ├── slicingProfiles
│   ├── timelapse
│   ├── translations
│   ├── uploads
│   ├── virtualSd
│   └── watched
└── plugins

Note: the /octoprint/plugins directory is the python libraries path, and /octoprint/octoprint/plugins is the path for plugin data and configuration. Prior to this change, both of these things existed in the /octoprint/plugins folder, polluting it's purpose.

This new method will allow savvy users to create distinct volumes for plugin binaries and octoprint configuration data, givinig them more ability to selectively control how state and memory consumption are utilized in their octoprint image usage/distribution strategies.