Add default values for from/size to document:search

[Aschen]

What does this PR do?

Explicitly declare default value for from and size in the request as specified in the documentation.
We have to be explicit otherwise the SearchResult returned can not be used as usual with the next() method.

const result = await this.sdk.document.search(index, collection, { query: 'some query', sort: 'some sort'})
await result.next()
// Unable to retrieve next results from search: missing scrollId, from/sort, or from/size params\nThis is probably not a Kuzzle error, but a problem with a plugin implementation.

[codecov]

Codecov Report

Merging #394 into 6-dev will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            6-dev     #394      +/-   ##
==========================================
+ Coverage   96.45%   96.46%   +<.01%     
==========================================
  Files          30       30              
  Lines        1440     1443       +3     
==========================================
+ Hits         1389     1392       +3     
  Misses         51       51

Impacted Files	Coverage Δ
src/controllers/document.js	94.91% <100%> (+0.08%)	⬆️

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