[FTS] Search index from import fails due to Field name 'content' has invalid value for field analyser

Steps to repro

1. Created a 3 node cluster with kv, n1ql and fts nodes
2. Created a couchstore bucket and loaded a few docs
3. Created a search index using UI
4. Copied the index definition preview from the UI
5. Deleted the search index, encountered MB-60075
6. Tried creating the same index using import using the definition copied previously
7. Index creation fails

Index created with 2 mapping child fields

1. field - content, type - text, searchable as - content, analyser - en
2. field - vector, type - vector, searchable as - vector, dimension - 384, similarity metric - dot_product

Import of the same index definition fails 

The index definition is as per this doc - 
https://cb-engineering.s3.amazonaws.com/MB-60076/search_index_definition.json