Add bridgedb_distributor field.

CHANGELOG.md

.../org/torproject/metrics/onionoo/docs/DetailsDocument.java

...va/org/torproject/metrics/onionoo/docs/DetailsStatus.java

...rg/torproject/metrics/onionoo/server/ResponseBuilder.java

...torproject/metrics/onionoo/updater/DescriptorHistory.java

.../torproject/metrics/onionoo/updater/DescriptorSource.java

...rg/torproject/metrics/onionoo/updater/DescriptorType.java

...ect/metrics/onionoo/updater/NodeDetailsStatusUpdater.java

...project/metrics/onionoo/writer/DetailsDocumentWriter.java

...roject/metrics/onionoo/updater/DummyDescriptorSource.java