Enable update checks through deployment-config without requiring the bundle-info.json of each bundle

[dragetd]

Is your feature request related to a problem? Please describe.
Right now, each bundle update is check by checking its bundle-info.json. If we could check the update through deployment-config.json, trivrost would not have to go through every bundle-info.json.

Describe the solution you'd like
We could add the field 'signature' to the bundle-info.json which would hold the signature that is usally loaded from the bundleinfo-json.signature location.

We could design this in a backward-compatible way that trivrost first looks for a signature in the bundle-info.json and if not found, reverts to the old behavior. (this would imply that once configured, the .signature files are ignored, which is intended.)

trivrost would also have to locally save the existing .signature files (which it is not doing yet) and compare them to the read signature. The signature should be unique for each bundle like a checksum (@ma-assbrock hopefully can verify this). Then we could skip the bundle-info.json download and trivrost would also start a lot faster usually.

Feedback welcome!