add celery example

examples/celery/requirements.txt

@@ -0,0 +1,56 @@
+#
+# This file is autogenerated by pip-compile with Python 3.10
+# by the following command:
+#
+#    pip-compile pyproject.toml
+#
+amqp==5.1.1
+    # via kombu
+async-timeout==4.0.2
+    # via redis
+billiard==3.6.4.0
+    # via celery
+celery[redis]==5.2.7
+    # via flask-example-celery (pyproject.toml)
+click==8.1.3
+    # via
+    #   celery
+    #   click-didyoumean
+    #   click-plugins
+    #   click-repl
+    #   flask
+click-didyoumean==0.3.0
+    # via celery
+click-plugins==1.1.1
+    # via celery
+click-repl==0.2.0
+    # via celery
+flask==2.2.2
+    # via flask-example-celery (pyproject.toml)
+itsdangerous==2.1.2
+    # via flask
+jinja2==3.1.2
+    # via flask
+kombu==5.2.4
+    # via celery
+markupsafe==2.1.2
+    # via
+    #   jinja2
+    #   werkzeug
+prompt-toolkit==3.0.36
+    # via click-repl
+pytz==2022.7.1
+    # via celery
+redis==4.5.1
+    # via celery
+six==1.16.0
+    # via click-repl
+vine==5.0.0
+    # via
+    #   amqp
+    #   celery
+    #   kombu
+wcwidth==0.2.6
+    # via prompt-toolkit
+werkzeug==2.2.2
+    # via flask