docs: Extend utils API docs coverage (#3402)

* Add more utils modules

* Format docstrings

* Incorporate reviewer feedback

haystack/utils/doc_store.py

@@ -16,7 +16,9 @@
 
 
 def launch_es(sleep=15, delete_existing=False):
-    # Start an Elasticsearch server via Docker
+    """
+    Start an Elasticsearch server via Docker.
+    """
 
     logger.debug("Starting Elasticsearch ...")
     if delete_existing:
@@ -37,8 +39,9 @@ def launch_es(sleep=15, delete_existing=False):
 
 
 def launch_opensearch(sleep=15, delete_existing=False):
-    # Start an OpenSearch server via docker
-
+    """
+    Start an OpenSearch server via Docker.
+    """
     logger.debug("Starting OpenSearch...")
     # This line is needed since it is not possible to start a new docker container with the name opensearch if there is a stopped image with the same now
     # docker rm only succeeds if the container is stopped, not if it is running
@@ -60,7 +63,9 @@ def launch_opensearch(sleep=15, delete_existing=False):
 
 
 def launch_weaviate(sleep=15):
-    # Start a Weaviate server via Docker
+    """
+    Start a Weaviate server via Docker.
+    """
 
     logger.debug("Starting Weaviate ...")
     status = subprocess.run(
@@ -121,8 +126,9 @@ def stop_service(document_store, delete_container=False):
 
 
 def launch_milvus(sleep=15, delete_existing=False):
-    # Start a Milvus server via docker
-
+    """
+    Start a Milvus server via Docker
+    """
     logger.debug("Starting Milvus ...")
 
     milvus_dir = Path.home() / "milvus"
@@ -146,7 +152,9 @@ def launch_milvus(sleep=15, delete_existing=False):
 
 
 def launch_milvus1(sleep=15):
-    # Start a Milvus (version <2.0.0) server via docker
+    """
+    Start a Milvus (version <2.0.0) server via Docker
+    """
 
     logger.debug("Starting Milvus ...")
     logger.warning(