feat(storage): load storage config for guided proposal

[joseivanlopez]

Add CLI support for setting and getting the storage config.

Load (set) storage settings from a config file:

$ agama config load < config.json

• The given settings must match the JSON schema defined by feat(schema): guided and AutoYaST storage proposals #1263 (not finished yet).
• The storage service calculates either a guided proposal or an AutoYaST proposal, depending on the given config.

Config for a guided proposal:

{
  "storage": {
    "guided": {
      "target": {
        "disk": "/dev/vdc"
      }
    }
  }
}

Config for an AutoYaST proposal:

{
  "legacyAutoyastStorage": [
    {
      "device": "/dev/vdc",
      "use": "all"
    }
  ]
}

Recover (get) the storage config:

$ agama config show > config.json
$ agama config edit

NOTES

• The storage service should check whether the given settings fulfill the JSON schema.
• Checking the schema is not done yet because the schema definition is not finished.

[coveralls]

coverage: 71.034% (+0.02%) from 71.015%
when pulling 2e3278b on load-guided-config
into b8e9ab2 on master.

[imobachgs]

np: I know we are kind of in a hurry, but in the future we should drop this call to unwrap.

[imobachgs]

Same than above.

[imobachgs]

What "schema" means? For me, the "schema" is the JSON specification. On IRC we decided to address this issue later.

[coveralls]

coverage: 71.412% (+0.4%) from 71.015%
when pulling 0059e2f on load-guided-config
into b8e9ab2 on master.

[coveralls]

coverage: 71.034% (+0.02%) from 71.015%
when pulling 0059e2f on load-guided-config
into b8e9ab2 on master.