Filtering through extractor with contenttype context attribute set

[littlesvensson]

• If a project that uses extractors in order to filter subscriptions to match against necessary criteria sends events with the "contenttype" attribute, RIG understands all these events as encoded ones and skips extraction of the data. As a result, no event is passed to the subscriber if an extractor is used, even though data sent to RIG are not encoded and all the criteria are met.
• It would be great if this could be changed in the future so that RIG checks if the data are really encoded or not, even if the cloudevent contains the "contenttype" context attribute.