Make key prefixes nice

Let's remember that keyname prefixes get used in the dashboard and are a common first impression that people have of the project. With that in mind it's important that, at least for common operations, these names are evocative and simple.

As an example, for `dd.read_parquet(...)` this should probably be "read_parquet" or "parquet" and not, as it is today "readparquetfsspec".

Start by tracing how key prefixes are generated for dd.read_parquet(...), then compare that path with other common operations. The change is done when common dashboard-visible keys use evocative, simple prefixes such as "read_parquet" or "parquet" rather than "readparquetfsspec".

Written by the indexing model from the issue text.