Make all doc fragments, module utils, and plugin utils private (#11896)

* Make all doc fragments private.

* Make all plugin utils private.

* Make all module utils private.

* Reformat.

* Changelog fragment.

* Update configs and ignores.

* Adjust unit test names.

tests/unit/plugins/module_utils/test__utm_utils.py

@@ -0,0 +1,66 @@
+# This code is part of Ansible, but is an independent component.
+# This particular file snippet, and this file snippet only, is BSD licensed.
+# Modules you write using this snippet, which is embedded dynamically by Ansible
+# still belong to the author of the module, and may assign their own license
+# to the complete work.
+#
+# Copyright (c) 2018, Johannes Brunswicker <johannes.brunswicker@gmail.com>
+#
+# Simplified BSD License (see LICENSES/BSD-2-Clause.txt or https://opensource.org/licenses/BSD-2-Clause)
+# SPDX-License-Identifier: BSD-2-Clause
+
+from __future__ import annotations
+
+from ansible_collections.community.general.plugins.module_utils._utm_utils import UTM
+
+
+class FakeModule:
+    def __init__(self, params):
+        self.params = params
+
+
+def test_combine_headers_returns_only_default():
+    expected = {"Accept": "application/json", "Content-type": "application/json"}
+    module = FakeModule(
+        params={
+            "utm_protocol": "utm_protocol",
+            "utm_host": "utm_host",
+            "utm_port": 1234,
+            "utm_token": "utm_token",
+            "name": "FakeName",
+            "headers": {},
+        }
+    )
+    result = UTM(module, "endpoint", [])._combine_headers()
+    assert result == expected
+
+
+def test_combine_headers_returns_only_default2():
+    expected = {"Accept": "application/json", "Content-type": "application/json"}
+    module = FakeModule(
+        params={
+            "utm_protocol": "utm_protocol",
+            "utm_host": "utm_host",
+            "utm_port": 1234,
+            "utm_token": "utm_token",
+            "name": "FakeName",
+        }
+    )
+    result = UTM(module, "endpoint", [])._combine_headers()
+    assert result == expected
+
+
+def test_combine_headers_returns_combined():
+    expected = {"Accept": "application/json", "Content-type": "application/json", "extraHeader": "extraHeaderValue"}
+    module = FakeModule(
+        params={
+            "utm_protocol": "utm_protocol",
+            "utm_host": "utm_host",
+            "utm_port": 1234,
+            "utm_token": "utm_token",
+            "name": "FakeName",
+            "headers": {"extraHeader": "extraHeaderValue"},
+        }
+    )
+    result = UTM(module, "endpoint", [])._combine_headers()
+    assert result == expected