version all the files, update CI tests and vscode settings

[dave-connors-3]

this PR

• adds versioned schema files for 1.5 + 1.6
• leaves the originals in place until we get the greenlight to deprecate them from @benmosher
• updates CI and the vscode settings to point the right versions at separate test files in the tests directory.
• adds dependencies.yml support in 1.6

[benmosher]

an idea: storing files as e.g. schemas/{version}/dbt_project-{version}.json would be the teensiest bit redundant, but as the versions pile up, you won't end up with one super-heavy folder fulla schemata.

[dave-connors-3]

@joellabes would love a quick re-review! I updated the folder paths per Ben's recommendation and added the matrix feature to make CI a lot DRYer. The only notable byproduct of that move was that schema.yml files in the tests directory are now named dbt_yml_files to match the name of the schema, so the matrix combos behave properly. Let me know if that is a dealbreaker for you in any way!

I also chose not to do the file regexing in validate_plusless_properties.py -- feels like a quarterly update of that variable as a part of the new version process is an OK amount of friction

[dave-connors-3]

@joellabes i didn't mean to dismiss your stale review :( i moved the default files back to the root of the folder so the IDE validation doesn't break