add dj.key_hash for working with jobs table

[ixcat]

Feature Request

Problem

Per discussion in datajoint/datajoint-python#862 & others, making dj.key_hash a public API for interacting with population jobs table will inprove usability of working with the jobs table when it contains many entries and users wish to investigate the status of a specific job.

Requirements

straightforward user interaction on the jobs table by primary key

Justification

See above

Alternative Considerations

current usage is as follows; requires need to index 32 into raw hash which is a bit of a 'magic value' from
the api consumer perspective

h = dj.internal.hash(key)
kh = struct('key_hash', h(1:32))
Item.Jobs & kh

Related Errors

n/a

Screenshots

n/a