Update getting started artwork (#20065)

Fixes #20031 by...
- Adds `create-environment.svg`
- Updates `python-interpreter.svg` for consistency with similar core
artwork
- Uses VS Code color variables to ensure artwork reacts to theme changes
- Removes redundant `v2` artwork asset

Note that the SVG previews in the diff below don't accurately represent
the illustrations since github.com can't pick up VS Code's CSS vars.

## Examples

### Select Interpreter

<img width="1143" alt="CleanShot 2022-10-25 at 12 37 21@2x"
src="https://user-images.githubusercontent.com/25163139/197867532-59d423d2-9ec0-4b5e-8b22-88916e7ff41d.png">

### Create Environment (no walkthrough step yet)

<img width="621" alt="CleanShot 2022-10-25 at 12 38 19@2x"
src="https://user-images.githubusercontent.com/25163139/197867560-d050c6a1-636a-45b2-a059-06f2ea554ac2.png">

### Theme support


https://user-images.githubusercontent.com/25163139/197867589-aaf9b93d-2900-457c-91f2-64837665fdd3.mp4

package.json

@@ -150,7 +150,7 @@
                         "title": "Select a Python Interpreter",
                         "description": "Choose which Python interpreter/environment you want to use for your Python project.\n[Select Python Interpreter](command:python.setInterpreter)\n**Tip**: Run the ``Python: Select Interpreter`` command in the [Command Palette](command:workbench.action.showCommands).",
                         "media": {
-                            "svg": "resources/walkthrough/python-interpreter-v2.svg",
+                            "svg": "resources/walkthrough/python-interpreter.svg",
                             "altText": "Selecting a python interpreter from the status bar"
                         },
                         "when": ""