This PR adds a few utilities related to Python interpreter detection:
- `python.DetectInterpreters` to detect all Python versions available in
`$PATH` by executing every matched binary name with `--version` flag.
- `python.DetectVirtualEnvPath` to detect if there's any child virtual
environment in `src` directory
- `python.DetectExecutable` to detect if there's python3 installed
either by `which python3` command or by calling
`python.DetectInterpreters().AtLeast("v3.8")`
To be merged after https://github.com/databricks/cli/pull/804, as one of
the steps to get https://github.com/databricks/cli/pull/637 in, as
previously discussed.
Serge Smertin