v1.2: Code sample changes

[maryamsulemani97]

1. Add get_documents_post_1 v1.2: Delete and get documents by filter documentation#2421

curl \
  -X POST http://localhost:7700/indexes/books/documents/fetch \
  -H 'Content-Type: application/json' \
  --data-binary '{ 
    "filter": "(rating > 3 AND (genres = Adventure OR genres = Fiction)) AND language = English",
    "fields": ["title", "genres", "rating", "language"],
    "limit": 3
  }'

2. Add delete_documents_by_filter_1 v1.2: Delete and get documents by filter documentation#2421

  curl \
    -X POST http://localhost:7700/indexes/movies/documents/delete \
    -H 'Content-Type: application/json' \
    --data-binary '{
      "filter": "genres = action OR genres = adventure"
    }'

3. Update get_documents_1 v1.2: Delete and get documents by filter documentation#2421

 curl \
    -X GET 'http://localhost:7700/indexes/movies/documents?limit=2&filter=genres=action'

4. Rename delete_documents_1 to delete_documents_by_batch_1

[maryamsulemani97]

@brunoocasali

This issue contains all v1.2 code sample changes. Could you please move it to the integration guide repo?