Fix unique index definitions

[jhoward-lm]

This PR contains fixes for schema unique index definitions and Document relations.

Document

• Use Metadata.ID string as ID
• Set Document as owner of its NodeList and Metadata edges (reverse edge.To() and edge.From() definitions in schemas)
• Store document ID (which is now Metadata.ID) as a field in NodeList schema

ExternalReference

• Fix unique index to include URL and Type fields

NodeList

• Fix unique index to include DocumentID field

Miscellaneous

• Fix backend debug option (client was nil at the time of calling its Debug() method)

[jhoward-lm]

@eddiezane @houdini91 @cpanato requesting review, I couldn't add to the reviewers directly

All changes are auto-generated except:

• internal/backends/ent/schema/*.go
• backends/ent/store.go
• backends/ent/backend.go
• Makefile

[puerco]

One non-blocking question but looks good to me

[puerco]

Is this breaking something with the client? or why would we not want to debug the client?

[jhoward-lm]

Yeah, at this point, client isn't initialized yet. It just sets the debug flag in the options, then in InitClient() this gets run:

	clientOpts := []ent.Option{}
	if backend.Options.Debug {
		clientOpts = append(clientOpts, ent.Debug())
	}

	client, err := ent.Open("sqlite3", backend.Options.DatabaseFile+dsnParams, clientOpts...)