Allow anonymous user in devcontainer name (rapidsai#1396)

Recently devcontainer names were updated to include the current user's name. However, in GitHub Codespaces, the username is not defined. As a result, the container name starts with a dash. This is not allowed by GitHub Codespaces, so it fails to launch.

This PR adds a default value of `anon` to the devcontainer username.

See rapidsai/cudf#15784 for more information.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Paul Taylor (https://github.com/trxcllnt)
  - Mark Harris (https://github.com/harrism)
  - James Lamb (https://github.com/jameslamb)

URL: rapidsai#1396

.devcontainer/cuda11.8-conda/devcontainer.json

@@ -11,7 +11,7 @@
   "runArgs": [
     "--rm",
     "--name",
-    "${localEnv:USER}-rapids-${localWorkspaceFolderBasename}-24.08-cuda11.8-conda"
+    "${localEnv:USER:anon}-rapids-${localWorkspaceFolderBasename}-24.08-cuda11.8-conda"
   ],
   "hostRequirements": {"gpu": "optional"},
   "features": {

.devcontainer/cuda11.8-pip/devcontainer.json

@@ -11,7 +11,7 @@
   "runArgs": [
     "--rm",
     "--name",
-    "${localEnv:USER}-rapids-${localWorkspaceFolderBasename}-24.08-cuda11.8-pip"
+    "${localEnv:USER:anon}-rapids-${localWorkspaceFolderBasename}-24.08-cuda11.8-pip"
   ],
   "hostRequirements": {"gpu": "optional"},
   "features": {

.devcontainer/cuda12.2-conda/devcontainer.json

@@ -11,7 +11,7 @@
   "runArgs": [
     "--rm",
     "--name",
-    "${localEnv:USER}-rapids-${localWorkspaceFolderBasename}-24.08-cuda12.2-conda"
+    "${localEnv:USER:anon}-rapids-${localWorkspaceFolderBasename}-24.08-cuda12.2-conda"
   ],
   "hostRequirements": {"gpu": "optional"},
   "features": {

.devcontainer/cuda12.2-pip/devcontainer.json

@@ -11,7 +11,7 @@
   "runArgs": [
     "--rm",
     "--name",
-    "${localEnv:USER}-rapids-${localWorkspaceFolderBasename}-24.08-cuda12.2-pip"
+    "${localEnv:USER:anon}-rapids-${localWorkspaceFolderBasename}-24.08-cuda12.2-pip"
   ],
   "hostRequirements": {"gpu": "optional"},
   "features": {