Linode: Mark 'name' as required. Fixes #29785 (#44699)

* Mark 'name' parameter as required.

Closes https://github.com/ansible/ansible/issues/29785.

* Add the `linode-python` dependency for unit tests.

* Add unit test for linode name parameter.

* Add note about where to find required arguments.

Closes https://github.com/ansible/ansible/issues/44696.

test/units/modules/cloud/linode/conftest.py

@@ -0,0 +1,13 @@
+import pytest
+
+
+@pytest.fixture
+def api_key(monkeypatch):
+    monkeypatch.setenv('LINODE_API_KEY', 'foobar')
+
+
+@pytest.fixture
+def auth(monkeypatch):
+    def patched_test_echo(dummy):
+        return []
+    monkeypatch.setattr('linode.api.Api.test_echo', patched_test_echo)