Update Python to 3.8.8 (#15278)

* update python fwlinks and remove bundle ver

* start fixing path for users with python 36

* prompt user for python version upgrade

* update python path after removing 3.6

* prompt users to upgrade and show pkg warning

* make prompt async

* remove python bundle ver from ML extension

* shutdown python 3.6 before deleting

* check useExistingPython before update prompt

* add dont ask again option

* remove 3.6 after installing 3.8

fix merge conflict

* give option to remove python36

* list user installed pip packages in warning

* create notebook to install pip packages

* update getPythonExePath method and add comments

* clean up code

* add comments

* pr comments

* add comment

* remove option to keep python36

* shutdown active servers before removing python36

* fix error removing old python w/ path change

* update to 3.8.10

* restart sessions for mac/linux

extensions/notebook/package.nls.json

@@ -4,6 +4,7 @@
 	"notebook.configuration.title": "Notebook configuration",
 	"notebook.pythonPath.description": "Local path to python installation used by Notebooks.",
 	"notebook.useExistingPython.description": "Local path to a preexisting python installation used by Notebooks.",
+	"notebook.dontPromptPythonUpdate.description": "Do not show prompt to update Python.",
 	"notebook.overrideEditorTheming.description": "Override editor default settings in the Notebook editor. Settings include background color, current line color and border",
 	"notebook.maxTableRows.description": "Maximum number of rows returned per table in the Notebook editor",
 	"notebook.trustedBooks.description": "Notebooks contained in these books will automatically be trusted.",