new searchPath setting

[eleanorjboyd]

new setting:
python-env.searchPaths: []
it can be the following:

• an executable (/bin/python directly)
• can be the venv folder (if its just a folder, we search /bin/python)
• can be a regex command (we will search for this regex command)

(Supports regex but you should warn that this could cause efficiency concerns.)

given searchPaths we then need to make a FINALSEARCHSET.

• first use await vscode.workspace.findFiles(xxxx, null); if there is a regex to find python. save the grand-grand folder of this executable and add it to FINALSEARCHSET
• next if there is a executable in searchPaths then get the grand-grand folder of this executable and add it to FINALSEARCHSET
• if the searchPaths item is a folder, just add it AS IS to FINALSEARCHSET

once we have FINALSEARCHSET we want to update configure in src/managers/common/nativePythonFinder.ts to include FINALSEARCHSET in environmentDirectories.

add some trace logging where needed. also when getting a final set and the environmentDirectories, make sure to remove duplicates.

[eleanorjboyd]

implemented this in the MVP form, will create a new issue when additional features are to be added