feat: add cli annotation subcommand (#2539)

add `cellxgene annotate` subcommand for invoking MLflow model to generate new `obs` annotations, initially intended for cell type annotations.

setup.py

@@ -9,6 +9,9 @@ with open("server/requirements.txt") as fh:
 with open("server/requirements-prepare.txt") as fh:
     requirements_prepare = fh.read().splitlines()
 
+with open("server/requirements-annotate.txt") as fh:
+    requirements_annotate = fh.read().splitlines()
+
 setup(
     name="cellxgene",
     version="1.0.1",
@@ -40,5 +43,5 @@ setup(
         "Topic :: Scientific/Engineering :: Bio-Informatics",
     ],
     entry_points={"console_scripts": ["cellxgene = server.cli.cli:cli"]},
-    extras_require=dict(prepare=requirements_prepare),
+    extras_require=dict(prepare=requirements_prepare, annotate=requirements_annotate),
 )