Search in history of a thing using RQL filter

[thjaeckle]

With the addition of #1498 (to be released in Ditto 3.2.0), it is possible to get a stream of all modification events of a thing (up to the configured history-retention-duration (e.g. 30 days).

It would be quite easy to enhance this new API in order to find a "special condition" within the history of a thing.
Examples:

• stream all events matching a given condition (filter as RQL)
  • e.g. in which a specific property was modified (via the SSE API):
    /api/2/things/namespace:my-thing1?from-historical-revision=1&filter=exists(feature/myFeature/properties/targetProperty)

Additional idea (optional):

• return the state of a twin when a certain condition (filter as RQL) matched
  • e.g. get state of complete twin when a given threshold was "first" reached:
    GET /api/2/things/namespace:my-thing1?filter-first-historical-revision=gt(feature/myFeature/properties/value,42)
  • e.g. get state of complete twin when a given threshold was "last" reached:
    GET /api/2/things/namespace:my-thing1?filter-last-historical-revision=gt(feature/myFeature/properties/value,42)
  • e.g. get timestamp when a given property was "last" modified:
    GET /api/2/things/namespace:my-thing1?filter-last-historical-revision=exists(feature/myFeature/properties/value)&fields=_revision,_modified