make `dlt init` to use `pyproject.toml` to setup workspace dependencies

[rudolfix]

Background
We could enable this when uv is present in the system and when we make our "new" workspace the default:

• instead of generating requirements.txt we would generate pyproject.toml (with uv)
• we'd actually initialize the lockfile with frozen dependencies as described in document best security practices for dependencies when installing dlt #957 (that could happen directly from uv.lock in the repo)
• we can easily add extras for a given destination (we do that for requirements file anyway)
• we can add dev extra to development deps to setup workspace properly