Add Dataset Activity.creation_action to ENTITY.Dataset as creation_action_activity

[ChuckKollar]

Issue #551

[shirey]

@yuanzhou instead of adding adding a new attribute would an on_read_trigger on the existing creation_action attribute which fills in the value work?

@ChuckKollar If possible I'd like to use the same creation_action attribute that exists already, but only currently used for POST operations, I think..

[DerekFurstPitt]

@shirey That was my thinking as well reading through this. If we still want this property to remain transient (for datasets) but want it to be returned on a GET request, I think an on-read trigger would suffice and wouldn't necessitate creating another transient property.

[DerekFurstPitt]

With these changes, this looks good to me.

[ChuckKollar]

OK! Great! Thanks for the suggestions and the read over! :-) I'm assuming that the current work satisfies Bill's change request.

[ChuckKollar]

This PR did contain the addition of the following code in src/instance/app.cfg.example

URL for talking to Ontology API (default for DEV)

Works regardless of the trailing slash

ONTOLOGY_API_URL = 'https://ontology-api.dev.hubmapconsortium.org'

But Joe wanted it removed, so I did.