Add an extra for setproctitle

This has always been optional, it seems it was just missed from
the formal specification of the extras.

Author: PeterJCLaw

poetry.lock

@@ -21,10 +21,12 @@ prometheus-client = "~=0.7"
 typing-extensions = "^4"
 redis = {version = ">=3.0,<5", optional = true}
 tqdm = {version = "^4.54.1", optional = true}
+setproctitle = {version = "^1.0", optional = true}
 
 [tool.poetry.extras]
 redis = ["redis"]
 progress = ["tqdm"]
+setproctitle = ["setproctitle"]
 
 [tool.poetry.dev-dependencies]
 # Testing tools