chore: remove cdktf from tests

[jsteinich]

Related issue

Fixes #8

Description

• Removes cdktf from the provider x command integration tests and instead tests using cdktn.
• Adds a way to fake the cdktn version for testing purposes so that we can test against the branch built code rather than a previously released version.
• Fixes an issue with C# package search.

Checklist

• I have updated the PR title to match CDKTN's style guide
• I have run the linter on my code locally
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation if applicable
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works if applicable
• New and existing unit tests pass locally with my changes