feat(18.1-01): task 2 taglist string mode, customTags and all save sites

- string mode: split on the separator (comma or whitespace), normalised,
  stored joined by a comma or one space; null stores an empty string
- customTags false refuses a tag outside options (taglist.not_allowed)
- taglist checked and hydrated on relation forms and settings forms;
  settings bind taglist columns; required checked on the tags
- admin: TaglistField string mode and closed option lists, preview renders
  the tags read-only as a comma-separated list; rebuilt dist
- docs: Taglist section covers both modes, separator and customTags

modules/cabana/testdata/catalog/models/badge/fields.yaml

@@ -9,3 +9,9 @@ fields:
         mode: array
         span: full
         options: [alpha, beta, gamma]
+        customTags: false
+    keywords:
+        label: Keywords
+        type: taglist
+        mode: string
+        separator: space