PLT-8131 (part2) Add plugin key value store support (#7902)

* Add plugin key value store support

* Add localization strings

* Updates per feedback

i18n/en.json

@@ -3554,6 +3554,10 @@
     "id": "app.notification.subject.notification.full",
     "translation": "[{{ .SiteName }}] Notification in {{ .TeamName}} on {{.Month}} {{.Day}}, {{.Year}}"
   },
+  {
+    "id": "app.plugin.key_value.set.app_error",
+    "translation": "Unable to set key value. See detailed error for more information."
+  },
   {
     "id": "app.plugin.activate.app_error",
     "translation": "Unable to activate extracted plugin. Plugin may already exist and be activated."
@@ -4242,6 +4246,14 @@
     "id": "mattermost.working_dir",
     "translation": "Current working directory is %v"
   },
+  {
+    "id": "model.plugin_key_value.is_valid.plugin_id.app_error",
+    "translation": "Invalid plugin ID"
+  },
+  {
+    "id": "model.plugin_key_value.is_valid.key.app_error",
+    "translation": "Invalid key"
+  },
   {
     "id": "model.access.is_valid.access_token.app_error",
     "translation": "Invalid access token"
@@ -6434,6 +6446,22 @@
     "id": "store.sql_team.update_display_name.app_error",
     "translation": "We couldn't update the team name"
   },
+  {
+    "id": "store.sql_plugin_store.delete.app_error",
+    "translation": "Could not delete plugin key value"
+  },
+  {
+    "id": "store.sql_plugin_store.get.app_error",
+    "translation": "Could not get plugin key value"
+  },
+  {
+    "id": "store.sql_plugin_store.save.app_error",
+    "translation": "Could not save or update plugin key value"
+  },
+  {
+    "id": "store.sql_plugin_store.save_unique.app_error",
+    "translation": "Could not save or update plugin key value due to unique constraint violation"
+  },
   {
     "id": "store.sql_user.analytics_get_inactive_users_count.app_error",
     "translation": "We could not count the inactive users"