Create reserved-entity-names.md

Created the file under the References section to display the list of reserved entities which we discourage users from using and may trigger a schema violation error if they attempt it.

app/_src/gateway/reference/reserved-entity-names.md

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+---
+title: Reserved Entity Names
+content_type: reference
+badge: enterprise
+---
+
+The {{site.base_gateway}} maintains a list of reserved entity names which cannot be used when naming workspaces or other entities.
+
+* `admins`
+* `applications`
+* `application_instances`
+* `audit_objects`
+* `audit_requests`
+* `ca_certificates`
+* `certificates`
+* `clustering_data_planes`
+* `consumer_group_consumers`
+* `consumer_group_plugins`
+* `consumer_groups`
+* `consumer_reset_secrets`
+* `consumers`
+* `credentials`
+* `developers`
+* `document_objects`
+* `event_hooks`
+* `filter_chains`
+* `files`
+* `group_rbac_roles`
+* `groups`
+* `key_sets`
+* `keyring_keys`
+* `keyring_meta`
+* `keys`
+* `licenses`
+* `legacy_files`
+* `login_attempts`
+* `parameters`
+* `plugins`
+* `rbac_role_endpoints`
+* `rbac_role_entities`
+* `rbac_roles`
+* `rbac_user_groups`
+* `rbac_user_roles`
+* `rbac_users`
+* `routes`
+* `services`
+* `snis`
+* `tags`
+* `targets`
+* `upstreams`
+* `vaults`
+* `workspaces`
+* `workspace_entity_counters`
+
+For example, a workspace cannot be named `consumers` or `vaults`. Doing so will yield a `schema violation` error response.