Add Observer class

[Aschen]

What does this PR do ?

Depends on #672

Add an Observer class to manipulate RealtimeDocument.

Those documents have the same structure as the Document object from the Document Controller except that they are connected to the realtime engine and their content will mutate when a realtime notification about changes is received.

const observer = new Observer(sdk);

// SearchResult containing realtime documents
let realtimeResult = await observer.search('nyc-open-data', 'yellow-taxi', { query }, options);

// Dispose ressources (realtime connection + memory)
observer.stop('nyc-open-data', 'yellow-taxi');

[lgtm-com]

This pull request introduces 1 alert when merging 8c5c0fc into 7cf06a5 - view on LGTM.com

new alerts:

• 1 for Unused variable, import, function or class

[rolljee]

since there is a stop method, i would call it stopAll () instead wdyt ?

[Aschen]

Actually I was thinking about having only one method that can take index & collection, index & collection & documents or nothing to stop subscriptions.
I will update and you can tell me

[rolljee]

LGTM, just a nit on naming convention

and also linting is surely necessary :)

[codecov]

Codecov Report

Merging #671 (f1f40c1) into 7-dev (948a042) will increase coverage by 0.32%.
The diff coverage is 88.39%.

❗ Current head f1f40c1 differs from pull request most recent head ffeca3c. Consider uploading reports for the commit ffeca3c to get more accurate results

@@            Coverage Diff             @@
##            7-dev     #671      +/-   ##
==========================================
+ Coverage   83.45%   83.78%   +0.32%     
==========================================
  Files          36       39       +3     
  Lines        1771     1881     +110     
  Branches      325      342      +17     
==========================================
+ Hits         1478     1576      +98     
- Misses        227      237      +10     
- Partials       66       68       +2     

Impacted Files	Coverage Δ
src/controllers/Document.ts	69.00% <50.00%> (ø)
src/core/searchResult/RealtimeDocument.ts	76.47% <76.47%> (ø)
src/core/Observer.ts	91.01% <91.01%> (ø)
src/core/RealtimeDocument.ts	100.00% <100.00%> (ø)

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[xbill82]

WIP Review