Fix inventory cache interface (#50446)

* Replace InventoryFileCacheModule with a better developer-interface

Use new interface for inventory plugins with backwards compatibility

Auto-update the backing cache-plugin if the cache has changed after parsing the inventory plugin

* Update CacheModules to use the config system and add a deprecation warning if they are being imported directly rather than using cache_loader

* Fix foreman inventory caching

* Add tests

* Add integration test to check that fact caching works normally with cache plugins using ansible.constants and inventory caching provides a helpful error for non-compatible cache plugins

* Add some developer documentation for inventory and cache plugins

* Add user documentation for inventory caching

* Add deprecation docs

* Apply suggestions from docs review

* Add changelog

lib/ansible/plugins/doc_fragments/inventory_cache.py

@@ -23,9 +23,13 @@ options:
     description:
       - Cache plugin to use for the inventory's source data.
     type: str
+    default: memory
     env:
+      - name: ANSIBLE_CACHE_PLUGIN
       - name: ANSIBLE_INVENTORY_CACHE_PLUGIN
     ini:
+      - section: defaults
+        key: fact_caching
       - section: inventory
         key: cache_plugin
   cache_timeout:
@@ -34,8 +38,11 @@ options:
     default: 3600
     type: int
     env:
+      - name: ANSIBLE_CACHE_PLUGIN_TIMEOUT
       - name: ANSIBLE_INVENTORY_CACHE_TIMEOUT
     ini:
+      - section: defaults
+        key: fact_caching_timeout
       - section: inventory
         key: cache_timeout
   cache_connection:
@@ -43,8 +50,23 @@ options:
       - Cache connection data or path, read cache plugin documentation for specifics.
     type: str
     env:
+      - name: ANSIBLE_CACHE_PLUGIN_CONNECTION
       - name: ANSIBLE_INVENTORY_CACHE_CONNECTION
     ini:
+      - section: defaults
+        key: fact_caching_connection
       - section: inventory
         key: cache_connection
+  cache_prefix:
+    description:
+      - Prefix to use for cache plugin files/tables
+    default: ansible_inventory_
+    env:
+      - name: ANSIBLE_CACHE_PLUGIN_PREFIX
+      - name: ANSIBLE_INVENTORY_CACHE_PLUGIN_PREFIX
+    ini:
+      - section: default
+        key: fact_caching_prefix
+      - section: inventory
+        key: cache_prefix
 '''