Rename from community.kubernetes to kubernetes.core (#6)

* Rename from community.kubernetes to kubernetes.core

This goes through and renames community.kubernetes to kubernetes.core.
Most of this was generated from the downstream build script that was
used on the community repository, plus whatever hand edits I could find
that were needed.

The downstream build and test process has also been removed as this
repository is now the downstream repository.

* Fix CONTRIBUTING.md

plugins/modules/helm_plugin.py

@@ -47,22 +47,22 @@ options:
       - Required only if C(state=present).
     type: str
 extends_documentation_fragment:
-  - community.kubernetes.helm_common_options
+  - kubernetes.core.helm_common_options
 '''
 
 EXAMPLES = r'''
 - name: Install Helm env plugin
-  community.kubernetes.helm_plugin:
+  kubernetes.core.helm_plugin:
     plugin_path: https://github.com/adamreese/helm-env
     state: present
 
 - name: Install Helm plugin from local filesystem
-  community.kubernetes.helm_plugin:
+  kubernetes.core.helm_plugin:
     plugin_path: https://domain/path/to/plugin.tar.gz
     state: present
 
 - name: Remove Helm env plugin
-  community.kubernetes.helm_plugin:
+  kubernetes.core.helm_plugin:
     plugin_name: env
     state: absent
 '''
@@ -96,7 +96,7 @@ rc:
 '''
 
 from ansible.module_utils.basic import AnsibleModule, env_fallback
-from ansible_collections.community.kubernetes.plugins.module_utils.helm import run_helm
+from ansible_collections.kubernetes.core.plugins.module_utils.helm import run_helm
 
 
 def main():