Install Pluto.jl and jupyter-pluto-proxy (#1929)

* Install Pluto.jl and jupyter-pluto-proxy

[Pluto.jl](https://plutojl.org/) is an alternative reactive notebook
frontend focused specifically on Julia. I think shipping this
by default in the julia-enabled images helps serve the Julia
community better, particularly when used with JupyterHub.

For context, I am working with the Julia users of the
[Jupyter Meets the Earth](https://jupytearth.org/) project, and
trying to understand how to best serve their needs on a JupyterHub.
We currently maintain a massive image that 'has everything', but
I'm trying to instead work upstream wherever possible so everyone
working in these subfields can benefit. Meeting Julia users where
they are at seems a useful path forward here.

* Add note about Pluto.jl to selecting.md

* Default to replacing - with _ in package imports

* Add jupyter-pluto-proxy to package import mapping

* Add Pluto.jl to datascience-notebook image

* Add test for pluto proxy starting correctly

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update test_packages.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ayaz Salikhov <mathbunnyru@users.noreply.github.com>

tests/julia-notebook/test_pluto.py

@@ -0,0 +1,32 @@
+import logging
+import secrets
+import time
+
+import requests
+
+from tests.conftest import TrackedContainer, find_free_port
+
+LOGGER = logging.getLogger(__name__)
+
+
+def test_pluto_proxy(
+    container: TrackedContainer, http_client: requests.Session
+) -> None:
+    """Pluto proxy starts Pluto correctly"""
+    host_port = find_free_port()
+    token = secrets.token_hex()
+    container.run_detached(
+        command=[
+            "start.sh",
+            "jupyter",
+            "lab",
+            "--port=8888",
+            f"--LabApp.token={token}",
+        ],
+        ports={"8888/tcp": host_port},
+    )
+    # Give the server a bit of time to start
+    time.sleep(3)
+    resp = http_client.get(f"http://localhost:{host_port}/pluto?token={token}")
+    resp.raise_for_status()
+    assert "Pluto.jl notebooks" in resp.text, "Pluto.jl text not found in /pluto page"