Write Metadata hosting service for Tests

[spannercode]

When registering dreps or creating proposals for tests, Metadata json must be publicly hosted.
We need a service to host those data.

Why

Using a metadata host service for testing instead of mock will make sure that the metadata-fetching, indexing or validating components of govtool are functioning properly.

Here is a deployed service URL:
https://metadata.cardanoapi.io/docs/

[mesudip]

PR is ready with the changes: #930