feat: add the JSON schema for the default Macaron buildspec

[behnazh-w]

Summary

This PR adds a JSON schema for the buildspec output and also adds a corresponding validation step for integration tests.

Description of changes

• Add the schema to the src/macaron/resources/schemas directory.
• Update the the documentation
• Add a validation step in integration tests and adjust the corresponding TypedDict for the buildspec.

[nicallen]

I notice that there is already one there, but I don't think our own schemas should be under src/macaron/resources/schemastore. That directory name is a reference to https://github.com/SchemaStore/schemastore specifically, for the schema file that we download from there (at build time in the Makefile), along with its LICENSE file as required by their license. Putting our own schemas in that same directory would suggest that those files are also under their license, which isn't our intention. Create a different directory for our own schemas (this new one and move the one that is already there), I suggest src/macaron/resources/schemas.

[behnazh-w]

I notice that there is already one there, but I don't think our own schemas should be under src/macaron/resources/schemastore. That directory name is a reference to https://github.com/SchemaStore/schemastore specifically, for the schema file that we download from there (at build time in the Makefile), along with its LICENSE file as required by their license. Putting our own schemas in that same directory would suggest that those files are also under their license, which isn't our intention. Create a different directory for our own schemas (this new one and move the one that is already there), I suggest src/macaron/resources/schemas.

Fixed in 006db30.