Issue #3480337 by bluegeek9: External Case Id

Closes #3480337

modules/crm_case_external_id/config/optional/field.storage.crm_case.external_id.yml

+langcode: en
+status: true
+dependencies:
+  module:
+    - crm_case
+  enforced:
+    module:
+      - crm_case_external_id
+id: crm_case.external_id
+field_name: external_id
+entity_type: crm_case
+type: integer
+settings:
+  unsigned: true
+  size: normal
+module: core
+locked: false
+cardinality: 1
+translatable: true
+indexes:
+  value:
+    - value
+persist_with_no_fields: true
+custom_storage: false