Update profiles schema to draft 2020-12 because as mentioned in https://github.com/microsoft/vscode/issues/98724#issuecomment-786502628, OpenAPI Specification 3.1 defines using JSON Schema 2020-12 and VS Code already has early implementation around it.
Basically, this just gets rid of the following error shown by VS Code when editing the settings.json file
```
Draft 2019-09 schemas are not yet fully supported.
```
## PR Checklist
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Schema updated.