BACKGROUND
Imagine you're working on 2-3 Salesforce projects each with a different target Orgs (sandboxes for different companies).
You're actively working on project 1 (coding, running tests, deploy source to the org etc) and in parallel to this, you need to make a couple of tweaks to project 2 and project 3 during the same time period.
Therefore you have 3 instances of Visual Studio Code open.
I realise I could run this command to tell SFDX which org is the default
sfdx force:config:set defaultusername=ALIAS_NAME
or
sfdx force:config:set defaultusername=name@example.com
QUESTION
Is there a setting in the project-scratch-def.json
that will tell Visual Studio Code which Org it should run the Salesforce DX against?