POC: Project schema validation

[kemmerle]

Description and Context

In this PR, I've created a very bare bones proof of concept for project schema validation in the VSCode extension.

For this little project, I've only added validation for app schema files in the new -hsmeta.json format. At a later stage, I will add logic to allow for validating more schema files.

Screenshots

With errors:

TODO

• Decide whether we want to break this off into its own extension (??)
• Add logic to allow for validating more schema files.
• Check in with BE team about status of public project schema endpoints.

Who to Notify

@TanyaScales @brandenrodgers @camden11 @joe-yeager