Add a "source" option for document:update to retrieve the updated document

[Yoann-Abbes]

What does this PR do?

This PR adds a source option. Set to true returns the updated document in a _source object.

Depends to kuzzleio/kuzzle#1549

How should this be manually tested?

Run Kuzzle within this branch kuzzleio/kuzzle#1549

document.update(index, collection, body, {source: true})

Other changes

Boyscout

[codecov]

Codecov Report

Merging #479 into 7-dev will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            7-dev     #479      +/-   ##
==========================================
+ Coverage   95.99%   95.99%   +<.01%     
==========================================
  Files          32       32              
  Lines        1298     1299       +1     
==========================================
+ Hits         1246     1247       +1     
  Misses         52       52

Impacted Files	Coverage Δ
src/controllers/document.js	95.23% <100%> (+0.07%)	⬆️

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[alexandrebouthinon]

👍 LGTM but missing a new end to end test to cover this use case

[Yoann-Abbes]

LGTM but missing a new end to end test to cover this use case

Functional test are in Kuzzle (which use the SDK)

[Aschen]

IMHO, unit tests are enough for a small improvement like this

[alexandrebouthinon]

Ok 🙂