Default ElasticSearch document repository settings do not work

[reckart]

Describe the bug
The default object type in the ElasticSearch document repository is texts, but it seems that ElasticSearch prefers _doc these days. So we should change it.

To Reproduce
Steps to reproduce the behavior:

1. Open a terminal and run ElasticSearch as a Docker service

$ docker run -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" -e "http.cors.enabled=true" -e "http.cors.allow-origin=http://localhost:9090" docker.elastic.co/elasticsearch/elasticsearch-oss:7.9.3-amd64

2. Open a second terminal and run ElasticVue as a Docker service

$ docker run -p 9090:8080 cars10/elasticvue

3. Open a browser and access ElasticVue at http://localhost:9090
4. Switch to the Indices tab in ElasticVue
5. Create an index named "test"
6. Switch to the REST tab in ElasticVue
7. Set the HTTP Method to "POST" and enter "test/_doc/1" as the Path (means "create a new document with ID 1 in collection test)
8. Put the following JSON into the request body field

{
 "metadata": {
   "language": "EN",
   "source": "repo",
   "timestamp": "date",
   "uri": "address",
   "title": "Test Document Title"
 },
 "doc": {
   "text": "This is a test document"
 }
}

9. Click "Run Query"
10. Start up INCEpTION
11. Create a new project "test"
12. Add a document repository with the following settings (and click save):

Name: "test"
Type: "Elastic Search"
Remote URL: "http://localhost:9200"
Index name: "test"
Search path: "_search"
Object type: "texts"
Field: "doc.text"
Result Size: 1000:
Random ordering: false

13. Switch to the dashboard and from there to the Search page
14. Select the repository "test"
15. Enter "document" into the search field and press the search button
16. I got a result for the document I posted to the ElasticSearch index in step 8
17. Click on import
18. INCEpTION produces a NullPointerException

Expected behavior
No exception.

Screenshots
If applicable, add screenshots to help explain your problem.

Please complete the following information:

• Version and build ID: 0.17.1