Prompt to turn on Pylint if a pylintrc file is found

[brettcannon]

This will be the only prompting under the language server.

[DonJayamanne]

Prescribed solution:

• Replace logic in isLinterAvailable method of linterAvailability.ts (src/client/linters/linterAvailability.ts) to check if the pylintrc file exists in the workspace folder

[ericsnowcurrently]

I was able to verify that this is done:

1. create a new folder with a simple spam.py in it
2. open the folder (and file) in vscode
3. select a Python interpreter/env that doesn't have pylint installed yet
4. set "python.jediEnabled": false in the folder's (new) settings.json
5. reload the window

Result: nothing happened

6. create an empty ".pylintrc" in the folder
7. reload the window

Result: prompted to install pylint

[DonJayamanne]

Changes required:

• Change message to You have a pylintrc file in your workspace. Do you want to enable pylint? [Enable] [Not now] [Do not show again]
• [Do not show again] - This applies to the current workspace
• [Not now] applies to the current session

[DonJayamanne]

This only works for .pylintrc & not for pylintrc.
Should support both file names.