fix: ensure python poetry envs are created when installing (#720)

- use pnpm instead of yarn for non-node projects.
- force usage of pyenv as a global dependency as this leads to more predicatable installs/builds and less errors to do with python aliases, etc 
- Ensure all non-node projects have their `install:ci` target called as part of the root `install:ci` script
- Ensure all python projects call `poetry env use pythonXXX` before installing to ensure the venv is setup correctly.
  - The logic here is to parse the `pyproject.toml` and fetch the listed `python` version. If it starts with a '^', we fetch the latest installed python version from the user's machine matching the major version. If the version is pinned, then we use that version.
 - Update docs to mention pyenv should be used.
 - Replace yarn with pnpm in getting started.

Author: agdimech

.projen/tasks.json

@@ -200,12 +200,12 @@ Other prerequisites depend on the language in which you develop AWS PDK projects
     - `YARN` [if `--package-manager` flag is unset]: https://classic.yarnpkg.com/lang/en/docs/install/#mac-stable
 
 === "PYTHON"
-    - `Python >= 3.9`: https://github.com/pyenv/pyenv
+    - `Python >= 3.11`: We highly recommend using [PyEnv](https://github.com/pyenv/pyenv) to manage your Python environments.
     - `Poetry >= 1.5.1`: https://python-poetry.org/docs/
-    - `YARN`: https://classic.yarnpkg.com/lang/en/docs/install/#mac-stable
+    - `PNPM >= 8.6.3`: https://pnpm.io/installation
 
 === "JAVA"
-    - `YARN`: https://classic.yarnpkg.com/lang/en/docs/install/#mac-stable
+    - `PNPM >= 8.6.3`: https://pnpm.io/installation
 
 ### Install the AWS CDK
 

docs/content/getting_started/index.md

@@ -5,7 +5,7 @@ import * as path from "path";
 import { TypeSafeApiProject } from "@aws/type-safe-api";
 import * as Mustache from "mustache";
 import { SampleDir } from "projen";
-import { NodeProject } from "projen/lib/javascript";
+import { NodePackageManager, NodeProject } from "projen/lib/javascript";
 import { ReactTypeScriptProject } from "projen/lib/web";
 import { ReactTypeScriptProjectOptions } from "./react-ts-project-options";
 
@@ -59,7 +59,7 @@ export class CloudscapeReactTsWebsiteProject extends ReactTypeScriptProject {
       packageManager:
         options.parent && options.parent instanceof NodeProject
           ? options.parent.package.packageManager
-          : options.packageManager,
+          : options.packageManager ?? NodePackageManager.PNPM,
       readme: {
         contents: fs
           .readFileSync(