[docs-beta] Add testable code snippets (#23836)

This moves our beta docsite code examples into its own folder under
`examples`. See instructions for how to run and test this.

Local testing, buildkite.

NOCHANGELOG

examples/docs_beta_snippets/setup.py

@@ -16,7 +16,7 @@
     packages=find_packages(exclude=["test"]),
     install_requires=["dagster-cloud"],
     extras_require={
-        "full": [
+        "test": [
             "pytest",
         ]
     },

examples/docs_beta_snippets/tox.ini

@@ -8,15 +8,15 @@ passenv =
     COVERALLS_REPO_TOKEN
     BUILDKITE*
 install_command = uv pip install {opts} {packages}
-# We install local packags to build from master, rather than pinning to a release.
 deps =
   source: -e ../../python_modules/dagster[test]
   source: -e ../../python_modules/dagster-pipes
+  pypi: dagster[test]
   -e ../../python_modules/dagster-graphql
   -e ../../python_modules/dagster-webserver
-  -e ../../python_modules/libraries/dagster-embedded-elt
   -e ../../python_modules/libraries/dagster-duckdb-pandas
-  -e .[full]
+  -e ../../python_modules/libraries/dagster-embedded-elt
+  -e .[test]
 allowlist_externals =
   /bin/bash
   uv